First of all you will need VirtualBox, not VirtualBox Open Source Edition (OSE). The latter doesn't support USB devices.

After installing VirtualBox 4 do the following in Ubuntu Maverick:

1. Go to System -> Administration.
2. Scroll down to "Users and Groups".
3. Open Users and Groups
4. Click "Manage Groups".
5. When the group settings menu pops up, scroll down to vboxusers. Highlight it. Click "Properties".
6. Check the box beside your user name below the part which says group members. Press OK.
7. Reboot.
8. Load Virtualbox, and USB should be enabled.