Usually the verdict is 1-4GB of Ram=32bit 4+GB of Ram=64bit , but I need to make sure I'm making the right choice. As a student, I have the choice of buying either the 32 or 64bit upgrade for Windows 7 (to be used via Bootcamp and VMWare). I've been using the 32bit and it seems to be working, but 64bit may be better. I'm using a Mid 2010' MBP (see sig) and the specs may be good enough that it handles the 64bit version better. I may also want to upgrade the RAM in the future so that's another thing to factor in.