As long as the 32-bit version you have is retail you're fine. MS will ship you a 64-bit version for only the cost of shipping, if I'm not mistaken. However, if your 32-bit version is OEM, you're out of luck. As OEM versions require you to contact your "system builder" for a 64-bit disc, I.E. yourself. I think you already know you can't supply yourself with one ; P