XP x64 was never compatible with McAfee home products unfortunately. You can obtain a refund under the 30-day money-back guarantee.
A Google search may find a substitute.
XP x64 being the first 64-bit OS, was really a proof-of-concept project for Microsoft where they tested 64-bit software/hardware for use in 64-bit Vista and later platforms. Although available to the public it was never intended for wide public use and people generally avoided it because at the time there was hardly anything that would work on it and very few motherboards/CPU's were designed for it. Back then it was an extrenely expensive choice so really only developers used it to test software/hardware. Of course as we all know a few years later and x64 is becoming very popular for its added security.