Vista 64 or Vista 32?? 4gb vs 2gb

well im going to be buying my pc today and im wondering which route i should take? vista 64 and 4 gigs of ram or vista 32 and 2 gigs of ram?

Im mainly worried about compatibility problems with my router, modem, speakers. I suppose they can be replaced. But right now i think vista 64 is a total wreck (thats my pre concieved idea).. however i want to go with 64 because there are less viruses and spyware.

so basically my questions are as follows:

1) can i still run all programs that i could on 32 bit?

2) will Diablo 2 LOD work lol?

3) is there a way to partition my hard drive (750 gig) to have both xp 32 bit and vista 64 bit??

and anything you could add

thanks for the help