The Windows XP Professional x64 Edition Technology Advancement Program enables customers who have purchased Windows XP Professional (32-bit) to exchange it for Windows XP Professional x64 Edition. You will need to have an x64 processor (the AMD Athlon 64, AMD Opteron, Intel Pentium 4 with EM64T, or Intel Xeon with EM64T) to run the new software.
Windows XP Professional x64 Edition Officially Live

Well, the wait is finally over. Windows XP Professional x64 Edition is finally, a real live, non-beta, official software release today! Current users of the 32-bit version of Windows XP Pro are eligible for a free upgrade, which is very unexpected from a company like MS, so take advantage, but ONLY after you have found all the necessary 64-bit drivers for your devices.