Ah. I had recommended CentOS as most newcomers to linux either don't have access to a RHEL subscription, or don't have the funds to pay for one.
If you already have an account with Redhat then I certainly would check to see what they have available!
Even for those without accounts Redhat provides freely-available documentation for their RHEL product (among many other linux topics), including installation guides, at http://www.redhat.com/docs/manuals/enterprise/
. These are available in html and PDF formats.
As a paying customer you also should be able to download the necessary .ISO image(s) to install RHEL on your computer; RHEL 5 update 4 is the latest build of which I'm aware, and I would use that unless you know you need RHEL4 for some specific backwards-compatibility.
Welcome to the world of open source software!