..and assuming that you are NOT booting with lilo, AND you are afraid of modifying grub's config, use the following:
Insert RH8 cd, and on the bootup-screen that says "welcome to RedHat Linux 8.0"
type "linux rescue" <ret> . then when it has booted into rescue type
"chroot /mnt/sysimage" <ret> and change any pwd's you like.
Never trust an OS you don't have the sources for.