is php installed? To verify please type the following from the Shell:
On a default installation of a Redhat like system, Apache comes with PHP built in. Apache needs ot be compiled with PHP support.
The command above will show you all PHP related packages on the system. PHP has either to be installed as an RPM package or complied from source.
Please look at apaches config file and verify the following line:
LoadModule php ....
Make sure that such a line is not commented since that's the line that tells Apache to use PHP as a model. PHP might installed but not enabled apache wise.