Is the PHP5 module enabled inside the modules.conf file that should be in (I believe) /etc/apache2?

modules.conf was apache1. Sorry.

So there should be a php5.load and perhaps a php5.conf inside the mods-available directory, and there should be symlinks to ../mods-available/php5.load and ../mods-available/php5.conf inside the mods-enabled directory. If the php5.load and php5.conf files exist, but the symlinks don't, then you can create them via the commands: ln -s ../mods-available/php5.load php5.load and ln -s ../mods-available/php5.conf php5.conf.

Note that I just tried this on my server, and installing the libapache2-mod-php5 package automatically created the files and symlinks for me... I don't normally use PHP myself. I believe I recall helping someone else out with this kind of problem (on his laptop), and his problems with PHP magically disappeared after a reboot.