you don't need to slipstream it if you just want to update some old machines (although they're run better for it no doubt)
don't slipstream in vista, it messes the PID, it's a known ms fault (and a massive one at that). unless you use nlite to do it, nlite does it fine
as for rebuilding the disc, i'd use nlite, if you're just slipstreaming & burning the disc, it doesn't touch any other files or inject any into the source..