Really should be the option: x64 CPU with x64 windows and mildly unhappy, because that's me! My PC runs like a dream but the driver issues send me bonkers (mainly cheap/old peripherals). When I go on to Vista Ultimate x64 the drivers should all come out, fingers crossed, and the issues will be minimal.
Generally if you've got higher that 1gb of RAM they say get x64. Don't bother becuase you can just wait for Vista. This is my opinion.