If you've got Mac OS X pre-installed on your Mac, you've also got php4 pre-installed. You don't need to download or compile anything. You just need to edit the /etc/httpd/httpd.conf file. Use the "sudo open -a TextEdit..." command line, above. Search for "php", and make sure you've un-commented _all_ the relevant lines: the two AddType lines above, and also the AddModule and LoadModule lines. (but not the AddType lines for php3, since you'll be using php4.) Save and restart Apache with "sudo apachectl graceful", and you are done.