Just a simple guide on how to get this necessary parts of lamp running on your centos 5.1 server.
First log in to the server as a user that has enough privileges to install via yum ( You might have to pop sudo in front of the commands if you are not logged in as root )
One of my colleagues at work wrote this post a while back but I think its relevance is something that should be nailed to some system admins foreheads at times 
http://brassy.net/2006/aug/backup_mxs_are_dangerous_and_pointless
Should you ever have the need to deploy a relay mail server that uses a mysql database to authenticate users for smtp auth this guide should see you through from the start to having happy users relaying through the server.
I’m writing a guide on how to do this at the moment and should have it up here in day or so….
EDIT
This is done now at http://www.bawkbawk.org/?p=4