Im not sure if using the PHP on IIS is a good thing for Apache, considering IIS setup can be quite different due to IIS not really suppose to be handling PHP. Try installing PHP again for Apache and see if all works. Also depending on your version you will need to put the php.ini file somewhere else other than
windows/system32
Depending on your version of Apache try putting it in the same directory that apache.exe is.
Apache 1.3x is the apache server directory.
Apache 2.x is the bin directory