If you installed onto a flash drive then the contents of the drive
will not be visible to Windows as it doesn't know anything about the
Linux file system - is this what you mean by not being able to read
the drive ? Or do you mean that Ubuntu will not boot from it ??

If you put Ubie on a flash drive. It can run just as slow as a live CD on older
systems. Just give it a little while.

I don't have windows, only ubuntu, but thankyou anyhoo

So when you say you used the flash drive to install Ubuntu then the
drive has a bootable installer of Ubuntu on it. Can you still boot
into this flash drive ? Don't need to go any further than that, just
confirm the flash drive is still readable anyway.

from windows with small free utility called Explore2fs you can easily access
Linux ext3 or ext2 partitions too without any problem.

Unless you do a full installation it will not be a Linux file system, but
likely FAT 32. The reason is that when unetbootin or Ubuntu's Startup Disk
Creator to install from an ISO it does not change the file system. It uses
what came with the usb key which is not likely ext. You can even create a
bootable Linux usb key from Windows by following instructions at
pendrivelinux.com.

When you do a full installation then it would need to create a Linux file
system and that is very different situation and I agree that Windows would
not be able to read it. It all depends how you create it and what kind of
usb key it is.

Ubuntu mounts flash drives as you insert them. You can access them from the
Places menu under removable drives or in the notification area under the usb
icon. Sometimes they will not mount properly. This often has to do with it
not being removed properly on the previous use. I have found it tricky to
get it to work in that session, but once it is mounted and removed properly
in another OS or after a re-boot it will often work fine.You can also try to
format it in Partition Editor if there is nothing on it. Occasionally a usb
stick just won't work any more in any OS.

Doesn't show up under places, mind that the usbs in the back work but not the
ones in the front. I'll try it my my sons pre-multi celled organism....I mean
computer, ;) He has Window 98