Nanobaud had it ABSOLUTELY correct, in that a BIOS-based dual-boot system is the best when you are testing a new OS. I cannot count the number of times that I have heard people complain that they set up a dual boot, wiped one of the OS', and then lost everything.... It is really quite simple too, just disconnect the original hard drive before you install XP-64 to the new one. When you are done installing XP-64 to the new one, shut down, reconnect the XP-32 drive, and then just pick in BIOS which hard drive boots first. I much prefer this to the Windows Boot Prompt, since I may only want to go to the testing OS every other day or so, or I may want to stay there for days at a time. This way, you only need to worry about switching over when you are ready to do so, and no need to untangle the boot listing for either one.