Basically, the publicly available version of Windows XP 64-Bit, which is still in beta, can only be used with AMD Operton and Athlon 64 based platforms. Its not possible to install the OS on anything other than an AMD.
So, basically it looks like if you are the lucky owner of a Nocona Xeon, then you still have some waiting to do. However, you will be pleased to know that a beta version of Windows compatible with Intel's 64-bit extensions technology is due within weeks.
Would you like to know more?