Um... ditch the IIS?
Here's an article howto get Apache/MySQL/PHP running on Windows
Check the forums and note all the issues people have. It never seems to work quite like it's supposed to. Also note the link i posted to PHP Home Edition, which worked the first time i installed it. SourceForge has several integrated packages that eliminate most of the hassle, this is just the one i grabbed. There may even be packages to integrate with IIS, i dunno.
It seems the most difficulty people have is installing on Windows. OTOH, i've compiled and installed all three on Linux box, and it always works just like the instructions. So what i'm saying is maybe on Windows, the easy way out is the ehm... easy way out. Especially if all you want to do is get to work coding.
You can run either Apache or IIS on an alternate port, if you want to keep both.