[SOLVED] how can i add a new user to virtual box

Hi am using the virtual box and trying to boot from usb iv'e installed the extension pact for usb but keep getting this message

Failed to access usb subsystem

virtualbox is not currently allowed to access usb devices. you can change this by adding your user to vboxuser' groups.
please see the user manual for more detailed information.

I cant seem to find the manual or where you add the user groups, by the way am using ubuntu 12.04 any help would be gratefully appreciated.