This is a script I use to start up a headless instance of virtualbox

Run as root but it fires the vm up as the user you use virtualbox as.

#!/bin/sh

# Output of "vboxmanage list vms"
# 
#"Windows XP Pro" {5998c1ff-f354-4d7d-b36d-987090351cb6}
#"JMITS LSMB" {ac08587f-b1d4-4767-a736-51adcb6f3f08}
#"Maps Dev - Debian 6.0.2.1" {9bb244ea-486b-471f-ad14-9df47c8c0157}

VM=9bb244ea-486b-471f-ad14-9df47c8c0157

su - userid -c "vboxmanage startvm $VM --type headless"

# where 'userid' is your username