Hands down the XP machine, no question. There are variables but Vista uses a lot of memory from the get go, even if you streamline it. The only exception may be if you get Vista 64 bit and can run more memory. I hear Windows 7 is supposed to be much faster than Vista. FWIW, this is based on a 3 laptop computer comparison. A memory intense trading program, and the kids playing Warcraft. - EZ