after a bit of time, I was able to get c5 installed and working on Windows XP Pro sp3, with php 5.2.13. If you have everything clean for install except the PATH_INFO error, then try this:
-----------------------------------
IIS -> website Properties -> Home Directory -> Configuration -> .PHP (edit) -> UnCheck - "Check that file exists" box

run this command/script from your c:\inetpub\adminscripts\ to update IIS:

"adsutil.vbs SET W3SVC/n/AllowPathInfoForScriptMappings 1" were 'n' is your website number, in XP PRO your default website is '1'

Add these two lines to your php.ini file:
cgi.fix_pathinfo=1
cgi.force_redirect = 0

restart IIS.

Hopes it helps.
-Frank