If you have an old PC lying around, download and install
Fedora on it, to work with while you learn. Fedora is RedHat without the logo.
If you don't have a machine handy, and want to get familiar with it via the command line, you can sign up for a XEN virtual server slice at
slicehost (my referral ID is shamelessly embedded in the link), have them build it with fedora, and then tweak to your hearts delight.