So i was thinking about getting WIndows 7

And finally get 64 bit if ONLY if your computer have over 4GB of memory, 32 bits can handle 4GB of memory.
(Also 64bits computers is slower by a small fraction of a millisecond because the memory address doubled, meaning it takes twice the amount of time for the CPU to process the memory address)

And I think you can only get 32 bit anyways, cause I read somewhere mac doesn't have 64 bit OS.

Most new computers have 4GB RAM. 32 bit computers can't actually make full use of the 4GB. 64bit is the future. It still has kinks of course, but there's really no reason not to upgrade now.