BadBlue's new Personal Edition has been tuned for XP Home. XP Home, of course, doesn't include any sort of web server. BadBlue is a freely downloadable web server that is a tiny download (just a little over 500K).

There is a wizard and illustrated tutorial for setting up PHP.

Free download of server - http://badblue.com/down.htm

Installing PHP and a server on your Windows PC - http://www.badblue.com/tuphp.htm

Writing your first PHP script - http://www.badblue.com/tuphp1.htm

Very easy to setup and it's so small you can carry it around on a floppy.