BTW, it's grub, not grup
Open up your grub.conf file. I believe it's located in /boot/grub, but I think Red Hat also has a symbolic link to it at /etc/grub.conf
In it you should see a line that starts with "splashimage". If you comment that line out, then you'll get a text-based menu next time you boot. If you want to get into the grub shell, that's something entirely different.
Try commenting out the splashimage, and if that's not what you want, we can mess with the config file some more. Or, if you don't want to wait for me, "info grub"