Hi:
Take a look to this:
Windows XP Home Edition Comparison Guide
<
http://www.microsoft.com/windowsxp/home/howtobuy/choosing2.mspx>
You can use the AMD Athlon 64 X2 Dual Core Processor in windows XP home as
long as you have just one CPU. Windows xp Pro can use a second CPU.
Your AMD will hovewer, use the Hyper-Threading feauture when running
Windows XP and Hyper-Threading
http://support.microsoft.com/default.aspx?scid=kb;en-us;810231
"Note: Windows XP Home can use a maximum of one (1) physical processor.
However, because Hyper-Threading is supported, the operating system takes
advantage of the second (virtual) processor."