Dual-booting Vista and OS X won't be much help if you want to play games, which was one of the major points of the post you replied to.
I don't know why you had so much trouble with XP though; it was flaky at first (which is why I stayed with Windows 2000 Pro for a couple of years after XP was released), but is now pretty solid. If you were having trouble with AV programs, then they were the problem and not XP as I have had no problems whatsoever with the AV software I use.
If the registry was getting screwed up, then you were almost certainly doing something wrong yourself (such as choosing to install malware-infested programs). Take a few minutes to find out about what you are considering installing first, and registry corruption will never happen. At least it hasn't happened to me in the entire time I've been using Windows 2000 and XP, and I've tried an amazing number of applications (including shareware and freeware). Install blindly and you're asking for trouble, regardless of which OS you're running.
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