It should work just fine either way, I always build for both.
Ok so I made a 32bit version (you can download it where the others are)
BUT, there is a high chance it will not work anyway.
I looked into that a bit more and it looks like there are problems with the newer Unity3D versions and Win7 (If that is the case you might just get a black screen)
I'm still looking if there is a way to get around this though, but there might not be one.