If VirtualBSD is running on a Dual Core system or better and the host computer won't be doing a lot of work while the virtual machine is running, you may get a nice performance boost by enabling a second core.
Search VirtualBSD 9.0.vmx for a line that reads (if the line is not present at all, just add it at the bottom of the file):
numvcpus = "1"
and change it to:
numvcpus = "2"
Save, exit the text editor and start VirtualBSD again. It should perform much better and, for instance, VLC will likely be able to play DVDs and videos smoothly.