First of all, I would recommend that you do not use Red Hat 9 for this as it's quite old and thus has some security problems. Fedora Core or another up2date distribution would be a much better choice.
What you need a HTTP server, namely Apache, an SMTP server such as Postfix and a IMPA/POP3 server such as Courier. For instructions on installing them, just search on Google.
You will also need a webmail package, SquirellMail is my recommended choice, althought it only works with IMAP by default.