PHP IIS problem

Hi I am a PHP newbie and am having a strange problem with PHP. I installed PHP using the windows install on my W2K server. I go to an html based page first, the php script will execute perfectly. If I go directly to a the php script I will get a page not found error. This happens with all php scripts. If I go back to that same php script that just ran, i.e. hit refresh, I will get a page not found error. I have tried isapi, setting the ntfs security on the PHP folder to allow full control for the IIS user. Anybody have any ideas? thanks roland campbell