The answers may vary based on what you'll be doing with the server, and what Red Hat product you'll be installing. Can we assume you're getting Red Hat Enterprise Linux 5 (RHEL5)? Have you looked at Red Hat's web site, under Support, Documentation?
I'm not the local Linux god, but Paul Sheer's "Linux: Rute User's Tutorial and Exposition" isn't a bad starting place. Google for it; it's downloadable for free.
You can get started before your server arrives. Download RH's Fedora product and load it on a test system. Fedora is RH's free, unsupported distribution (distro) and is close enough to RHEL for you to use as a learning tool.
Once the local Linux power players notice this question you'll get plenty of suggestions to keep you busy.