Well, there shouldn't necessarily be another account with root access - that's not the best idea to have lying around. Besides, who would know that password if they couldn't remember root's?
Some systems, you can boot into single user, and "be" root without knowing the root password.
On many systems, you'll have to boot on mini-root or off of some media (floppy, cdrom, etc) depending on your version on Unix. Since I am not familiar with Tru64, I can only suggest what may possibly help in a generic fashion.
1) Boot into single-user, mini-root, floppy, disk, or whatever
2) mount the device holding your /etc partition
3) edit the passwd file (or shadow if you're using shadow passwords) to remove the root password altogether
4) boot normally, and change root's password to one you'll remember!
Keep in mind that this possibly won't work if you're using something like NIS, or if the OS doesn't store passwords in a flat file like passwd or shadow.
Search
Google for details on how to boot into single user, or off of another media.