I also run XP pro and IIS, although I ditched pretty much everything to do with what came with IIS and configured it for my own file.
In my C:\WINDOWS\ php.ini file:
cgi.force_redirect=0
doc_root=
TBH I just used the PHP installer and checked the cgi.force_redirect=0 on the advice of a friend and left it at that. Try it and see if it works.
Just a point - isn't this an installation issue?