You don't need apache... XP ships with IIS.. go to add/remove prgrams, add/remove windows components, and then through the list, under internet tools (or something to that effect) you will see Internet information Services.. add that and reboot...
Then go to Run, TYPE compmgmt.msc You will be in the computer manangement console.. then expand services and VOILA, you will see your web server installed and mapped to C:/inetpub/wwwroot..
Then run the PHP installer for windows.. thats the easiest (but not the most robust) way..
Yu will need ISAPI for the most robust, but that may be too much for you right now if your new to IIS.