Hm. Try top from a term - or ktop or whatever your environment is - and check out the pids. If X is 50, do 'kill 50'. I suppose that would drop you out, though I'm not sure if I've ever tried to kill X from in X.
Yeah - that worked for me - I don't have X in CORE, but fired up BasicLinux - and, weirdly, X was 50.
Crap. Sorry - I misread. The problem is you couldn't see how to do all that. Lemme think. *smoke pours out*
Okay - maybe 4th edit's the charm. I assume you have your installation disks/floppies? Just use those. It's Red Hat - there's got to be an option for you to use them to boot, stop the installation process, and go to a 'fix' mode, right? Or you have some kind of boot disk? Or can download one? Any good rescue disk ought to boot directly to console, anyhow.
(Incidentally, first thing I do, when I have X is change the default runlevel - I *don't* like booting into anything graphical.)