You can run Vista in a Virtual PC on the same computer for free!

I ran across this article and this relates to using a virtual installation...with Ultimate or Business Vista, you can load another instance of Vista on your computer....something to give some thought to with all the new capabilities available with virtual installations...just make sure you have enough ram...great way to try out some of the "cloud" services too without risking your initial installation...and run other health care applications without one interfering with the other...BD

In Windows Vista, the license agreement states that the licensed copy can be installed in a virtual PC on the same computer as the licensed computer. So now you can install Vista once and then install it again in Virtual PC without having to buy another license!!!
However, this will only be available for Windows Ultimate or Business editions, not the Home or Home Premium editions! So if you’re interested in using Vista virtually to avoid permanent changes to your personal computer (it’s a great way to avoid viruses and spy ware when browsing), then go for the Ultimate edition and the it’ll pay for itself as you’ll have two copies running instead of one!
And corporations will get even better benefits; the Business edition will allow up to 4 copies to be run on the same computer!