VPC 2007 Seems to work really well with MS OS's. I tried linux distro on it, and it doesnt like it - wouldnt boot. If you want it for non MS operating systems try virtual box by Sun - that works well too, and free.
I have a Q6600 and 4 Gs of RAM, and it runs very nicely. Another prob is that it only ever assigns one core to the VM and you cant seem to change that. Maybe you can, but its not obvious.