Have you followed the instructions at
https://help.ubuntu.com/community/VirtualBox ?
USB in VBox is not enabled by default and you need to do a little
command line jiggery pokery to get it working - the web page above tells
you how to do it (and it does work, for me, at least

The point of that page on which I focused is the USB section, as I said
on my previous message, since all the rest seems to work properly.

If your VB install is up and running (USB included), could you give me a
tip of what should I check next?

Well, if you've followed the instructions there and you still don't have
USB, I'm at a bit of a loss.

I assume you're running the PUEL version, rather than the free one, as
the free one doesn't support USB.

Did you add the Guest additions for VirtualBox? It adds the ability to use usb
devices, cut and paste and to move the mouse in and out of the guest window
without having to press the right-Ctrl key.

Yes, Guest additions are added.

More on that issue:

Here's how my USB is set:

br.geocities.com/marcelotodaro/vb_usb_filters.jpg

Following someone's suggestion I removed all but one filters and left it
unchecked:

br.geocities.com/.../vb_usb_filters_2.jpg

Whether or not the box is active results are the same after restarting
the virtual machine: no USB device available.

But hey! I found something interesting. I removed the last filter, then
I disconnected the webcam, connected a pendrive and restarted the
virtual machine. This is what happened:

br.geocities.com/marcelotodaro/vb_usb_devices.jpg

Note that VirtualBox detects USB devices connected to the hardware but,
no matter there are or are not filters for them, it doesn't make them
available.

Does that say anything to you? (I wish it did to me...)

The only time I have run into something like this is for usb devices that the
host cannot handle. For example, I have a music player that Linux does not
recognize. It won't work in a Windows VM running on Linux because the host
cannot detect it and pass it along. This would not appear to be the case in your
situation since the devices show and you say they are detected. As was said
previously some versions of VirtualBox do not support usb shared devices, but
your version shows them so it must support usb device sharing.

I saw your thread on VirtualBox forums. There are a couple of good points made
here. One is mounting. If it is mounted in the host then it will be unavailable
in the guest (except for CD and DVD drives where you have pass through enabled).
Secondly you can control which ones are available to the guest once they are
unmounted in the host from the menu bar of VirtualBox. By checking the boxes
here they are enabled for use in the guest OS.
If you cant get it going you have other options such as VMWare server.

Well that's how things were suppose to work but they don't in my case.

Which makes me wonder: since I can't get proper help anywhere I should
be the only one facing such problem, otherwise there would be more help
available. What could possibly be wrong on my install then? Why VB see
my USB devices but just don't make them available?

Odd, isn't it?

> If you cant get it going you have other options such as VMWare server.

Well VMWare is a paid piece of software. If I have to pay for it I
rather prefer to buy a new scanner that works on Ubuntu, which is why I
installed VB and Windows.

I also have the problem that my USB devices seem invisible to the guest
operating system (I think that I am using the correct terminology). I
actually don't care very much and just stage anything that I need through
shared folders.

But no, you are not the only one with the problem. Perhaps you are the only
one who really needs the USB access!

VMWare Server is free. You just have to provide an email address when you
register and the provide you with a free license number. It will expire, but it
has been free for several years now. I still prefer VirtualBox for ease of
installation, but VM server is still good.

The first step is to check which version of VirtualBox you are running. Not all
support usb sharing. You want PUEL, not OSE. See this link:
https://help.ubuntu.com/community/VirtualBox

Next you need to have Guest Additions installed in the guest OS. Then there are
a few minor things to do such as unmounting the device you want from the host to
make it available in the guest. And then, if you were following the thread,
there are no guarantees that it will work. However, I have had good success and
so have others.

I don't think that I had noted the point that the device must be
un-mounted on the host OS. Perhaps this will solve my problem.

But actually, as I said, I am not particularly concerned about this problem
and am very happy as I am and have no great need to use the USB under the
guest OS. I will merely trying to reassure the original poster that it was
not a problem unique to him (or her?)

Incidentally I am running VirtualBox twice - Windows XP under an Ubuntu host
and Ubuntu under a XP host. Both work great.

But I finally got the mistery solved: the Group ID from VBOX wasn't in
the USBFS-Entry. More detail here:

http://forums.virtualbox.org/viewtopic.php?t=10661

What a difference from VB for Mac OS X! It was just ready to use with
all its funcionality (USB included) right after the install was done.

Sometimes I wonder why things on Linux need to be such a pain...

To be fair, I've used every version of Windows from 2.0 to Vista and
I've had similar, apparently trivial but actually major problems with
all of them. The difference being that, with Linux, you can get under
the hood, if necessary, to solve them but with Windows you usually can't
and so end up getting more and more frustrated. (Never used a Mac, so I
can't comment).

On the whole, I prefer Linux. Yes, it can be frustrating. Yes,
sometimes finding the information you need can be somewhat akin to
having your teeth pulled - without anaesthetic! But, for me, at least,
the problem solving is half the fun.

Anyway, great news that you've got it working and thanks for posting the
answer. I've learned something new today and no day in which you learn
something new can be called totally wasted .

There are other options. You could use another OS where installation is easier,
but you would have a file system that can be compromised easily unless you are
willing to devote most of your waking hours trying to keep out intruders.

It is a trade off. With Linux you get a system that is modular and powerful. We
use scripts, daemons and modules in place of a centralized registry that can
become damaged and gets fragmented. Most users don't need all of the features
and power users will find ways to do take advantage of them. Most do not fear
the commandline after awhile. So don't think of it as being hard, but as having
power at your fingertips.
In addition with Linux you get choice which means that Linux has lots of
variety. This makes it more difficult for vendors such as Sun (VirtualBox) to
tailor their products. Maybe someday there will be more standardization, but
don't count on it. Linux users are an odd lot. They like choice and dislike
being told that there is only one way. It is the quickest way to get a reaction
from Linux users. Just try to limit their choices and you will find out. They
don't want there to be one kind of Linux or one way to do anything. They want
both the GUI and the commandline. They to be able to choose the distro that
suits them best. They want it all.

You got that right. Linux isn't just an OS. It is a cult. Just kidding. We do
come across as zealots and are a bit cultish sometimes. To newbies we must seem
to be treating it like a cause. But most Linux users are advocates because it is
the only way we can spread the word. We have no advertising campaigns like "I'm
a PC", no front man like Gates or Jobs, and no retail presence. So we fill in as
best we can. If we didn't display our loyalty then it would be hard to know that
Linux exists.