I think I finally have an answer. I build my own pcs so I always buy my OS as a retail package. The machine I'm trying to load now with slipstreamed XP (made from retail package original disk) is a laptop that came with an OEM version of windows XP. Seems that MS has a different key code scheme between the two. My understanding now is that if I slipstreamed my OEM version it would work for my laptop and maybe only that laptop. Retail seems to work on any of my machines as long as I use the correct unique key code. So for now I'm loading with original cd and adding SP2 and other updates the old fashioned way.