PHP5 wasn’t working right out of the box for me in OS X Leopard, so here is what I did to fix the issue. Fire up your trusty terminal window and type (you can replace “mate” with whatever editor your comfortable using, like pico or vi):
mate /etc/apache2/httpd.conf
find the line that reads:
#LoadModule php5_module libexec/apache2/libphp5.so
and remove the ‘#’, save the file, and reboot apache by turning off and on again under System Preferences > Sharing > Web Sharing.