Nowhere on the Vista site does it differentiate between the 32 bit and 64 bit editions... are you sure it's a 64 bit OS? In the upgrade matrix there is no upgrade path from the 64 bit XP... just sounds kinda backwards if you ask me.
My understanding is that the installer will check to see if your CPU is 64-bit capable. If it is, it will install the 64-bit version, if not then it installs the 32-bit.
Vista is geared for 64-bit, so most hardware support will be written for 64-bit. 32-bit will probably just have to get by with default MS drivers. There is already talk about devices such as HD/Blu-Ray DVD drives not going to be 32-bit compatible.
This also explains why XP-64 driver support sucks. Few users use x64, so hardware makers are concentating on Vista 64-bit drivers, rather than x64. I have x64 on my media server, and I can't get drivers for my network printer or scanner (both HP & both less than 1 year old). If I want to print anything from it, I have to use my MFC/fax machine shared on another computer.