I've been using 64-bit Windows for ages now (XP 64 and now 7 x64) and not had many problems. The odd piece of old hardware not working (a cheap old webcam, nothing important lol).
I installed Windows 7 x64 when I had 2Gb of RAM because I was planning on getting 4Gb (which I've now got). I agree with bmj2728
and say that if you can run x64, you should. Mainly because I think that eventually 32-bit software will become thin on the ground (maybe not for a while mind lol).