You can trade-up your 32bit windows to 64bit XP from now until July 31, 2005. Before you take the plunge however, you need to make sure you can track down 64bit drivers for all the stuff you use. This is a clean install only, so migrating data is up to you.
Here is a nice quote from the Technology Advancement Program site: "Purchasing technology can be frustrating—the minute you buy something, the new version becomes available. We understand this frustration..."