Did you create a separate /boot partition. If you installed RH with an LVM volume, the kernel is needed to assemble the volume. If you created /boot inside the LVM volume, you created a catch 22 situation.
If not, you can enter in the kernel and initrd lines manually, and try to boot up. This isn't as hard as it sounds because grub includes auto-completion. Typing in "kernel " and pressing the TAB key, you will be presented with choices. E.G. enter "kernel (hd" and press TAB.
You will be presented with the drives names. Grub uses names like (hd0) for the first drive, and (hd0,1) for the second partition of the first drive.
Suppose that /boot is on the 3rd partition of the first hard drive. Enter "kernel (hd0,2)/" and press enter. The auto completion will present the files in the selected partition. If you see files such as vmlinux and initrd, you found the correct partition.
With luck, you will be able to boot up. From here you can try to correct the problem.
Another option is to boot up with the install disk and enter "rescue" to enter the rescue mode.