Try putting in your redhat disc, and starting up as if you were going to install. Then, once at the first screen, you should be able to press enter or something else, maybe F1. Press F1 for help might be the wording. So press F1, then if you read through the options, you should have a "rescue" option. So type rescue, then enter. This will take you into rescue mode. Mount the drive, in say, /mnt and then you will need to access the /etc/passwd file. In there you will see a user called root. Delete the X in roots entry. Now go ahead and restart, root will have no password, so you will need to make a new one.