If you don't have official Windows 7 driver support, its a hit or miss if Vista and built-in drivers in 7 will work. If you want to mess with that, get a new hard drive, SSD if you have the money, and install Win 7 on it. If it does not work, pop in your other drive and you're set.
Before you go messing with 64bit, see what the max RAM for your system is. You should not feel the need for more than 4 gig of RAM for a few years I'm thinking. By that time the CPU and video card will seem much slower than any lack of RAM anyway.