Setting up a mail server

I need a roadmap for setting up a mail server using RedHat 6.2. What config files do I change? I have a peer network currently. Do I need to setup DNS? I would like my users to use MS-Outlook for a client to send and receive mail. I would also like to fetch mail from a dialup ISP and add it to each users mailbox as needed. The HOWTO’s are great but I need basic knowledge on how to start!