Step 1: install virtualbox

Do not use apt-get of "sudo apt-get install virtualbox"
get following guide
http://www.virtualbox.org/wiki/Downloads
http://www.virtualbox.org/wiki/Build_instructions

Step 2: add yourself to virtualbox group
sudo adduser $USER vboxusers

Step 3: fstab
sudo vi /etc/group
...

based on ubuntu 7.10 / 8.04 / 8.10/9.04

Step 1 (ubuntu 7.10/8.04):
sudo vi /etc/init.d/mountdevsubfs.sh

Find these script:
#
# Magic to make /proc/bus/usb work
#
#mkdir -p /dev/bus/usb/.usbfs
#domount usbfs "" /dev/bus/usb/.usbfs -obusmode=0700,devmode=0600,listmode=0644
#ln -s .usbfs/devices /dev ...