I’ve been quite smitten by VMWare lately — their free products, natch — and have sunken quite a few hours into playing around with it. It’s really coming in handy for test PCs when I want to look into a feature; I now have one PC with a stack of VM images on it which can be fired up if I need to check out something on a particular OS. Another nice feature of this is making a separate copy of an image to test just a single application — handy if you expect that application to horribly break things.
In addition to the free tools — VMWare Server (previously MSX) and VMWare Converter Free — VMWare have just announced that the next version of their small-footprint hypervisor enabled ESX server (ESXi) will be made available free (read about it Here). No doubt in response to increasing competition in the Virtualization market, this is still a real boon for testers as well as SMEs.