I foresee some problems. You *can* install WUBI to an external drive, but it
is going to present you with a couple because usb drives are removable and
because the file system in WUBI is inside a large file.

If you have more than one USB device attached WUBI may not work. The
bootloader will be on your C: drive on the MBR. It will point to WUBI
thinking that it is fixed in that location. However, if more than one device
is attached the bootloader may point to the other device. The bootloader is
set to a fixed location, but usb devices can be removed and that could be a
problem in some circumstances.

Secondly you will not be able to access the file system on the usb device
other than through WUBI because WUBI is just a large image file, like an
ISO. Externally you won't see your home folder just the image file. You can
add to the device from Windows but they would not appear in Ubuntu as they
would be outside the image file. You can add to the device from Ubuntu and
they would not be available in Windows because Windows cannot access inside
the image file. Copying your /home folder to Ubuntu while your in it is not
going to work very well either because some files will be in use. It is a
Catch-22.

A better solution would be to go for a full Ubuntu installation on the
external drive. If you have a boot manager, ie. can press a key on boot up
to choose which drive to boot, then write grub to the external drive and not
the MBR of the C: drive. This way, you can control things better. You can
copy the home folder without difficulty using the Live CD which won't work
for WUBI because the file system is hidden to you. If you don't have a key
to press to get a boot manager then you can write to the C: drive MBR, just
knowing that it may give you problems if more than one device is attached.

WUBI is not meant to be a substitute for a full installation. It is meant as
a way of testing Ubuntu that gives more of a full experience than the Live
CD which cannot be written to. You can use it in the way that you want, but
it is awkward to say the least and in the long run it will limit you more
than you realise.

Ok, I understood about half of that.

Please tell us what things are still a mystery to you and I'm sure
someone will give a simplified, more detailed, explanation. We really
want to help!

Let's start with what WUBI is. It is a bit of wizardry that creates a large
file in your Windows file system. When you re-boot it offers to load
Ubuntu. But Ubuntu is installed inside the large file and not on a drive or
partition. The boot loader treats it like the file is a drive and mounts it.
Once Ubuntu boots then it appears normal because you are now inside the
large image file. Windows can never see inside the file from the outside. It
can only see the large file. Therefore you can't put anything inside the
file from the outside. That also applies from the Ubuntu Live CD. The only
way that you can add to the large file is from the inside. That presents you
with a problem. You want to copy files to your home folder from an external
source (which is possible), but some of those files won't let you because
they will be in use. You will start getting error messages and will quickly
become frustrated. Data files will not be a problem, but your settings will
be.

If Ubuntu was installed to the external drive not using WUBI everything
would be accessible from the outside because you can see the actual files
and not just a large container file. Then you could copy the home folder
while the files are *not* in use. I would use the Live CD to do that and it
would be easy.

The second problem has to do with the bootloader. A bootloader is a snapshot
in time. It says that this is where Windows can be found and this is where
the usb drive can be found. But let's say that you have a usb key and your
external drive plugged in. Then it may get it right or may not. It does not
guess it just looks where it originally was, but if the usb key is there
then it won't look elsewhere for WUBI. It just gives you an error message.
You would have to unplug the usb key and re-boot.The bootloader is just a
file and it cannot keep track of changes made after the fact.

My advice was to do a regular installation because the file system can be
seen and manipulated from the outside. Whether you write the bootloader to
the default location is up to you. It is just easier to manager if it is
written to the same device as it is installed on from my own experience.

Sorry for making it sound complicated. I hope that by understanding what
WUBI is that you can see how it works. There are additional problems with
WUBI that make it unsuitable. It is a large file that can become corrupted
if the power goes out or you crash. If you are in regular Ubuntu it is not a
large file but a file system made of lots of little files. You may lose
something small, but not everything.

Ok, so if I get an external HD, and I install Ubuntu regularly on that drive,
letting Ubuntu use the whole thing, then I would just have to make sure the BIOS
knows to check for the external drive to boot from first, right?

I planned on using Wubi because I can get the latest release and updates that
way online, rather than an old CD or DVD with an older version or minus all the
updates.

Is there another way to download Ubuntu? Say, from a website to a DVD, then
install from there to the external drive? And then before I delete my Ubuntu
installation of the existing HD, from there I copy /home to another DVD and then
load it onto my external drive? Or just make a copy of /home and tell Ubuntu to
write it to the external drive?

Does that sound like a plan?

Your BIOS would have to be able to boot from usb *only* if you write grub to
the external drive. If you use the default and write grub (the Linux
bootloader) to the C: drive then the answer is no.

Once Ubuntu is installed you can get updates online in the same way that you
did with WUBI. (Other than the way they work you would notice no difference
once you are in Ubuntu.) The latest Ubuntu (now only in Alpha 2) comes on CD
*and* DVD, but it is not ready for prime time till the end of April. The
latest stable version(10.10) comes *only* on CD, but you can update as you
install and then after re-booting you can add whatever else you want.

The usual way to get Ubuntu is to download the ISO then burn it to CD or
DVD. I use DVDs even for the CD version cause they are cheaper and easier to
come by.

First back-up: If you have lots of room on your C: drive then I would copy
the files that you want from WUBI to a temporary folder on C. That way I
would have them in case WUBI no longer worked. Note: A regular Ubuntu
installation will overwrite the Windows bootloader which allows you to boot
WUBI. If you don't have lots of room then you will have to cross your
fingers or think of something else. Then once the regular Ubuntu is
installed you can copy the files from C to Ubuntu's home folder on the
external drive. Once you are sure that everything works from the external
drive you can remove WUBI from the Windows Control Panel (Add and Remove
Programs) and delete the temporary folder.

Things that may help:

http://www.ubuntu.com/desktop/get-ubuntu/download
https://help.ubuntu.com/community/BurningIsoHowto
https://help.ubuntu.com/community/Installation

Been there done that. If the drive is not connected when you start up
the computer can get lost.

Suggestion;
get a large flash drive like 32g and install Ubuntu on that giving the
rest of the drive for storage. In this way the grub is not installed and
you still have a full functioning OS on the external device.

IMHO you would be better fitting a larger HD to the laptop, cloning
the current contents after removing Ubuntu then installing Ubuntu
under WUBI again but giving it more space to play with on the larger
drive.

If you get a Seagate or Western Digital HD then they both have a free
version of Acronis True Image that can handle the cloning from the old
HD - just put the old HD in a USB caddy and plug in before firing up
Acronis, it will happily clone from a USB attached drive.

Also - why not go the whole hog and get the latest Ubuntu and install
that under WUBI if you must use it that way instead of dual booting ?

get a large flash drive like 32g and install Ubuntu on that giving the
rest of the drive for storage. In this way the grub is not installed and
you still have a full functioning OS on the external device.

There are different levels of fast. You need to use a fast one like Class 8
or 10. I run my netbook on a 16 GB Class 8 SD card and it is fast enough. My
home folder is on the 160 GB HD. I have run it on a no name usb key and it
is usable, but not great. I prefer the SD card to usb key because it is
harder to dislodge.

I apologize for the brief interjection, but would you
mind speaking towards the longevity of the SD card with
Linux installed? I ask because I have often wondered if
there would be any issue the considering the limited write
cycles of the card and frequency of writting that happens
with Linux. My brain tells me it should be no different than
running from a USB stick, but others have argued that SD
cards are worse. I just don't know enough about that stuff
to know which is more accurate.

I've had this one for about three years. It is name brand, top of the line
back then. Now they have class 10 and maybe higher. It runs pretty much non
stop.

If you are determined to use and external drive then consider e-SATA
as an option - it's as fast as a full SATA and there are 2.5" ones
that will take a laptop drive and aren't too large to carry around.