If you have any older programs that you simply must use, and the world would stop if you couldn't, research them and determine if they're either vista compatible, or if there is an alternative.
Even if there are older programs that you simply must use, and you can't find an alternative, just create a safe dual booting system, and be merry.
Vista is fine, works really well, and is stable-ish. It may take some getting used to, but in the end, it is designed to be more user friendly than any previous windows os.
You're definately going to want to disable UAC, or it'll drive you nuts, like over %50 of the users out there.