There is a known problem between Ubuntu Lucid (as host OS) and Virtualbox (3.2 for sure).
Didn't you know it? Well, I didn't know anything about it either until an hour ago... :-)
Basically it all works fine except the USB controller. Virtualbox doesn't allow you to access any USB device on the guest OS. They are all greyed out...
If you have the same symptoms it's likely that you have a permission problem.
Check that the user you are logged in with is a member of the group "vboxusers".
The procedure can easily be done trough the GUI.
System -> Administration -> "Users & Groups"
Click on "Manage Groups" and scroll down at the bottom looking for the "vboxusers" group and check if your user is listed. If it's not, well, you simply need to add it... :-)
NB: In some cases you might have to restart your machine.