hmm... if the httpd.conf stuff is all good, then I'd be interested to know if Apache is even loading the php module. go in the libexec folder in your apache install, and rename the "libphp4.so" file, and stop and restart apache. did it start with no errors?... if so then PHP wasn't configured and installed correctly.
if your apache is compiled with modssl, then there's another possibility that i've seen in the past-- php alters the httpd.conf in a funny way, so that the LoadModule and AddModule calls are inside an <IfDefine SSL> block. if that were true, and you started apache w/o ssl, you would get the behavior you describe.
