The ipod is right now syncing with the itunes library I have on another USB based Western Digital external hard drive - perfectly - within Windows XP running as a guest of the host Ubuntu 9.10 using VirtualBox -
Which overall means I can now use iTunes & my ipod classic etc with Ubuntu 9.10
If your currently having problems similar to my old one here your problems may? be different, so this solution may? not directly work for you (but then it might!) - so I am going to give you the full information as to how I got it all working for me from the starting point of this entry ( ie the USB can be seen in VirtualBox but not in the guest Windows XP OS)
I am using the very latest version of VirtualBox - VirtualBox 3.0.10 for Ubuntu 9.10 ("Karmic Koala") i386 (ie for an intel processor) under the PUEL licence ie via
http://www.virtualbox.org/wiki/Downloads - that is downloading the VirtualBox binary (program) from the options at the top of this page. The open source version available at the bottom of this download page
does not include support for using USB ports - so don't select /use this is you want to use a USB connection. The PUEL is still free (as in money) for non commercial home use (see the wikipedia entry for VirtualBox for more information on this licence)
My problems were resolved by initially following the advice given by Etepetete in his comment above, this led me to google ipod site:forums.virtualbox.org and deciding to work through each page returned - the first page
http://forums.virtualbox.org/viewtopic.php?f=2&t=17288 gave me the clue I needed - this suggested running 'itunes diagnostics' & that the problem was with running USB 2.0 devices - one of the menu options in iTunes is 'itunes diagnostics'- so I selected this -
Remember at this point the ipod could be seen in VirtualBox (ie not greyed out - to get to this point the Ubuntu user you are logged in as must be assigned to the various groups etc - as in my first post here) but note : I could not see the ipod in Windows Explorer or iTunes.
iTunes diagnostics led to a display saying the ipod was not found & a help button - pressing this led to an apple ipod advice web page full of help for resolving these problems
http://support.apple.com /kb/TS1369 & this led to me running - Click the Start menu and click Run. Type “devmgmt.msc” and click OK - which showed windows XP device manager. (there are other helpful links on the apple web site for Mac & other guest operating systems)
In windows XP device manager looking not just under USB devices but under other sections I found one device with a ? in yellow by it (indicating a problem with it) - right clicking this led to discovering that this USB device did not have a driver - click a get a driver button led to a microsoft wizard to go & get a driver for this device (I believe it found it on the Internet). This led to the drivers for the USB 2.0 ports being automatically installed after 5 minutes of activity & since then windows XP programs (explorer & iTunes) have been able to see all USB 2.0 devices with out a problem & work with them just fine - problem solved & all is working 100% as expected / perfectly
I'll add some screen shots below of my adventures described above - a picture tells a thousands words kinda reasoning:

I