I have tried the 32 and 64 bit versions and have had two components, a Hauppauge 950 hdtv tuner, and my old Canon A20 camera, not install because driver couldn't be found. Windows found 32 bit drivers automatically.
64 bit version, to me, seemed slightly sluggish (instantaneous responsiveness) vs. 32 bit on same rig, but then again I am not running super power computing parts (e7200, 4 GB RAM, XFX7600GS, and WD6400AAKS), so ymmv. Also tried installing 64 bit on less powerful system (Shuttle SG31G2 with Celeron 440, 2 GB RAM, WD6400AAKS, and stock integrated graphics) and it seems to struggle a bit (vs XP Pro); haven't tried installing 32 bit version yet.
I don't need 4 GB RAM or more for my needs, so I think I am leaning to 32 bit for possible greater compatability with legacy components and electronics (?)