I am building a VDI environment this spring. So naturally I was looking to setup a FreeBSD client as well in the virtual environment. I discoverd that VirtualBox does not ship with FreeBSD virtualbox-additions, and was a bit disappointed. Then rememberd that there is a Virtualbox-OpenSource Edition of VBOX for Freebsd. ( in /usr/ports/emulators )
I have now built the VirtualBox-OSE client and is using it with FreeBSD 8.2 i386 as a client on a Windows workstation. Next step is to try it out on the Solaris host that runs the production VDI environment.