After shutting off firewall ( if any) and sweeping/removing spyware, shut off ALL unneccessary background progs-eliminate BG prog as potential source of prob, and game will play better with a freed up cpu at the least: http://www.blackviper.com/
Rats , you did say you have xp, right? Shouldn't need xp re install yet. First shut of the 30 odd progs running you don't need, including any " little strangers" you may have in the background.
You may find a simple first step google " windows startup inspector" freeware, dl to desktop,easy to use first step to see/turn off programs, it rates whether you need it running.