I am currently using a Apache configuration with Mysql and PHP. MySQL
is usually considered a more simple database, and by many better than
Postgresql.
MySQL is probably either already installed, or on one of your redhat
cds. You may have a little hassle getting it running, but it's all good
once you figure it out. PHP is almost always bundled with Apache, and I
think it's even in the default distribution. Yes, php is the best way
to interface with a database, and it's also very good for other web
scripting.

The de facto place to find Linux/Unix software is freshmeat.net, for
your future software needs. (and yes, their search engine is pretty good.)