Go into single user mode. When in grub, instead of allowing it to boot, make sure your current OS and kernel are selected and press 'e'. This will allow you to edit the boot options.
You will see the grub config. just find the line that tells grub what kernel to use and add 'single' to the end of it and press 'Enter' and your changes will be saved. Now, when it boots, you will be in single user mode and it wont start the X server.
If that doesn't work out, try downloading a live CD like knoppix. Boot into the live cd, mount your / partition and edit the /etc/inittab file of your RH9 system to boot into runlevel 3:
Look for this line:
Make it look like this:
X will not startup.
Of course,with either option, make sure you change your settings back when you are done or you wont get your X server running on boot.