While I use VPC 7 for some work-related Windows stuff, just for kicks, I downloaded .iso images from
Knoppix.net and
Ubuntulinux.org.
Of course, the nice thing about VPC is that you can "grab" an .iso image as an actual CD and so what you essentially are left with is a run-time, HD-based Linux image that requires no additional installation and can be fired up reasonably quickly.
Still some networking issues (getting the systems to see the VPC network adapter) but something to do if you wanted to test VPC out with alternative systems.
Now only if I could get BeOS to boot correctly without having to burn a physical CD...