Try Googling the error phrase. You may find some helpful items, or you may not. There were a lot of articles, but I am not certain how they apply to you.
Anyhow, check your IIS to make sure you have your virtual directory setup right, and that you have the *.php extension allowed for that virtual directory.
Also, you may want to look into installing Apache instead of using IIS... I switched from IIS on WinXP to Apache, and my scripts run faster and better. In addition, I opened up my scripting options with things like the mod_rewrite functionality in Apache. Just my 2 cents.