I am sorry for the inconvience caused to install McAfee software.
Could you please let me know the version of XP (Pro,Home) and the Service pack of XP installed on your PC, also i would like to know if XP is up to date ( Internet explorer > Tools/Safety > Windows update), install updates if available.
Please download and run MCPR tool using the link below :
After which re-start your computer once and then try downloading McAfee software.
Hope these steps helps you to fix your problem, if you have already performed these steps then let me know....
McAfee Technical Support