VMware Player - Run any virtual machine
VMware Player lets you evaluate new or pre-release software contained in virtual machines, without any installation or configuration hassles. You can also share existing virtual machines with colleagues or friends—just use VMware Player to run any virtual machine.
http://www.vmware.com/products/player/
I've been playing with this on my Xp machine. Pretty cool. So far I have been able to run Fedora Core 5 Test, SUSE 10.0, OPenBSD, Ubuntu, plus a number of LiveCDs.