PHP is a separate package to install from Apache. Open Yast, and do a search for PHP; you should find a package called "apache2-mod_php4", and another just called "php4" (among loads of others).
Select those two packages, and any others in the list you want (I would always include things like php4-pear and php4-session, as they're quite commonly used, but your choice of individual modules is up to you)
I can't remember whether Suse 9.3 came with PHP5 as well (10.0 does). If it does, you will be able to install either php4 or php5; just pick the appropriate packages for the version you want.
Hope that helps