Seems to be best supported right now (package in Debian, optional drivers for Windows, starting unmodified VMWare machines -- after you guess right settings that is!)

Links

• Windows ACPI problem - agp440.sys problem
• How to migrate existing Windows installations to VirtualBox - it's applicable to other emulators as well!
• Creating and Configuring Headless VMs in VirtualBox

Debian Install

OSE version (no USB!) comes in Debian, compile vboxdrv with:

root@llin:~# module-assistant a-i virtualbox-ose