Hi Kaz,
I am using Vista Ultimate 32 bit on this pc which I use for every day stuff.
I have XP on a second pc that I use for storing films, music and other data on and use that connected to my TV to watch downloaded TV and Films and anything in HD.
I also use it for recording TV on and converting and editing AV stuff so that I can surf and do other stuff on this pc without slowing anything down.
I like Vista and dont seem to have the problems that some people are having with it. The only reason that I havent got Vista on the other pc is that I havent got around to it yet and havent really got the time to reinstall all the programs on it.
I dont think that XP has the same features for setting user permissions as Vista has although you could possibly do something similar by creating a guest account in XP.