My httpd.conf had some of the lines, but not all of them -- mine was missing the LoadModule and AddModule lines for php. I'm not sure why -- I don't delete any of those; I just comment them out if I'm not using them. Plus, the note above put a space in "LoadModule"; it has no space. I didn't know about the "apachectl graceful" trick, though -- since "httpd -k restart" stopped working (probably around 10.2), I had just been doing it manually -- find the process, kill it, and hit httpd again -- thanks for the tip!
So for those who are missing any of the lines, here are the full lines.
In the section with all the other LoadModules:
LoadModule php4_module libexec/httpd/libphp4.so</div>
Directly below that section should be the AddModules; you need:
AddModule mod_php4.c
And then the AddType lines should be right after the language priorities (so after the AddCharset lines and after the LanguagePriority bit):
AddType application/x-httpd-php .php
AddType application/x-httpd-php-source .phps
Then restart apache/httpd as described above, and hopefully you should be good.
BTW, the actual module should be at:
/usr/libexec/httpd/libphp4.so
So if things fail, you can check to see if that's there.
Thanks to others who posted here; it definitely helped and got me on the right track. I just had to find the module manually to write my own LoadModule line.