As far as I remember, the GUI is started from /etc/inittab under RHEL. Open /etc/inittab and you should find that the last 1 or 2 lines in the file are the ones that start X in runlevel 5. It's the one that has the following in it: /etc/X11/prefdm Comment out the line(s) and then your system should boot without X. But, as suggested in the previous posts, it probably best you just go to runlevel 3. Or, if you really want to, you could customize runlevel 4 to do this.
The following link gives you detailed information about the RHEL boot process: http://www.redhat.com/docs/manuals/e...n-process.html