Edit the X configuration file in /etc/X11. Goto the section "Screen" and remove every "1024x768".
Code:
modes "1024x768" "800x600"
becomes
Switch back to X (<ctrl><alt><F7>) and restart X with the combination <ctrl><alt><backspace>.
On RH it's probably something like XFree86-Config or so. And first make a backup of the X configuration file.
PS you should be able to cycle through the different resolutions using <ctrl><alt><-> and <ctrl><alt><+>