Supersite for Windows takes a look at Vista's 64-Bit support

The x64 versions of Windows Vista adopt all of the positive and negative quirks of their XP x64 predecessor and add a few wrinkles of their own. Like XP x64, the various Vista x64 versions support x64-compatible PCs based on the AMD-64 (Athlon-64, Opteron, Turion processors) and Intel EMT-64 (Pentium D and Xeon) platforms. Unlike XP x64, you don't need to buy a x64-specific versions of Vista. Instead, all Windows Vista editions, except for Vista Starter, will come with both 32-bit (x86) and 64-bit (x64) versions in the box, on separate DVDs. This includes the Home Basic (and Home Basic N), Home Premium, Business (and Business N), Enterprise, and Ultimate editions of Windows Vista.

Windows Vista Feature Focus: 64-Bit (x64) Support