you should always do a search first - I believe there's been a lot of threads concerning this matter.
Anyhow, you can't run vista in parallells legally unless you buy one of the two most expensive versions (business and ultimate if memeory serves me right) - the macpro should have enough juice to run both vista and mac os x - just don't expect it to run as well as if you would run it without virtualisation (as in starting windows by itself).