Vista 64 will work fine just install AH into a folder other then "Program Files (x86)." I suggest using a folder like 'Program Folders' because you want to avoid the UAC relocation of AH files.
You might want to go down your list of hardware before moving to Vista. The more affordable sound cards dont work well with Vista. The ones I know work with Vista 64 are the SB XiFi Fatality Titanium and Xonar and BGears bEnspirer (which I use). I cannot recommend on-board sound with Vista 64 because plainly speaking it sucks and your game will screw up.
The only game that I am aware of that benefits from Vista 64 is FSX SP2 (or Acceleration) which uses multi-cores and is large address aware (can use more memory). Crysis might also I just never checked into it but it does have a 64-bit executable. Direct X 10 is not enough reason to move to Vista 64. You can enable other games and programs to utilize more memory but you have to really know what you are doing and it involves risks of its own.
DrDeath go take your medicine.