I would guess that 64 bit would be best.. I have a late 2008 mackbook pro with 2.5 gHz processor and 4 gigs of RAM.. I do notice that the 64 bit version requires more hd space though and that's a bit of premium for me.. I guess what I'm really thinking about is how much of a difference will there be? I'm basically gonna be using windows for 3ds max and gaming so preformance would be a primary concerned. So I think I just answered my question. But I'm curious if people have experience of how noticeable the difference is btwn the two?