If you have more 4 GB or more RAM, the answer should be clear to you already.
QOTD: Are You Going 32 or 64-bit for Win 7? : Read more
QOTD: Are You Going 32 or 64-bit for Win 7? : Read more
In my experience, this is only true on retail and upgrade versions, not OEM, unless they changed it for 7. I bought a 32 bit windows vista upgrade, and had to order the 64 bit media for 'free' + a $10 shipping and handling charge.Thankfully, both 32- and 64-bit versions are included in the same package, so you won't have to commit one way or another until you pop the disc in the drive.