Actually people Vista will run faster for multi-core processors but Xp will always beat Vista in older PC's. As Vista was designed for the multi-core setup as Xp doesn't support it the only reason to go vista is to maximize CPU utilization on multi-core CPU's and DX10. Otherwise stay with XP it needs less hardware power than Vista ever will.
BTW Windows 7 not 07 is rumored to be close to release so the suggestion to wait for Windows 7 is actually one recommended by most techs.
