I don't think I had to anything, not that I can remember anyway.
RH8 puts an extra config file in /etc/httpd/conf.d/php.conf which contains the directives to start PHP.
This file contains the following:
<br />LoadModule php4_module modules/libphp4.so<br /><br /><Files *.php><br /> SetOutputFilter PHP<br /> SetInputFilter PHP<br /> LimitRequestBody 524288<br /></Files><br /><br />DirectoryIndex index.php<br />
Make sure the php module is in apaches server directory, on my system it is located here:
/usr/lib/httpd/modules/libphp4.so