The VirtualBox in the repositories (OSE) is not full featured. To get all of
the features (such as usb support) you need to full or PUEL version from the
VirtualBox website. Download the full version which is free to individuals.
(See: http://www.virtualbox.org/wiki/Editions)

http://www.virtualbox.org/wiki/Linux_Downloads

Choose the right architecture for your distribution. For Ubuntu it will be
for either 9.04, 8.10 or 8.04 and AMD64 or i386. The file will be a .deb and
you can install it by clicking on it.