I downloaded and installed VirtualBox on my Debian Etch laptop and I experienced a permissions error the first time I tried to start a virtual machine, however it worked fine running as root. The fix is easy and was found in the FAQ of the VirtualBox website.
If you get a message saying “VirtualBox kernel driver not accessible, permission problem” when starting VirtualBox right after installation, make sure that your user account is listed in the vboxusers group. The installation takes care creating that group, but you will need to manually add all users to it that should be allowed to run VirtualBox. As root, for each such user, run usermod -G vboxusers -a . If any of the affected users are currently logged in, they need to log out for the changes to take effect. In case any user already attempted to start VirtualBox before logging out (which launches the VBoxSVC service process with incorrect permissions), that user additionally needs to run VirtualBox shutdown from the command line to terminate the service. This solves the permission problems. (Alternatively, a reboot will help as well.)