Is apache compiled to run php as a dynamic module (DSO) or as a static module? Type httpd -l to get a list of compiled in modules...
If php is compiled as a dynamic module, your httpd.conf should contain the following lines:
LoadModule php4_module libexec/libphp4.so
AddType application/x-httpd-php .php
If somewhere in your httpd.conf file you have a ClearModuleList line then you also need this line:
AddModule mod_php4.c
If php is compiled as a static module you'll need this line in your httpd.conf:
AddType application/x-httpd-php .php
Check that your php.ini file is in the appropriate place and edit it if necessary.
If you installed apache and php as rpm's, you might find the best solution is to uninstall them then download the source packages and compile them yourself.