Are you using the php module or the php CGI? If you're using the php CGI, you need to specify it as the handler for .php files in apache's config. If you're using the module, make sure apache's config has a LoadModule line to load the php4 module. Make sure that your scripts end in .php
Also make sure you've got the right configs. I don't know exactly what happened, but over the years, the RH server at work ended up with two completely different apache confgs and 3 php.ini files, of which only one of each did anything, and everyone was too scared to erase the extra configuration files.