Sources who have been examining the latest build of Longhorn (the code name for Microsoft's latest incarnation of the workstation stream of Windows), which is supposedly due in Q4 of next year, say that it has "extensive support for the AMD 64 (Hammer) family of CPUs."
Longhorn, which will probably wind up being called something like Windows XP 2 or something like that, includes a completely redesigned and reworked Windows user interface. Its supposedly meant to be even easier to use than previous Windows versions, and of course its gonna look a lot cooler and run a lot slower... ;)
"Not that Longhorn won't support IA64 (Itanium) microprocessors from Intel, though. According to the source who is close to Microsoft's plans, both 64-bit CPUs will be supported when the product is released," writes The Inquirer, here.