How to Regain Root Password Using Grub Commands

From http://forums1.itrc.hp.com/service/forums/questionanswer.do?threadId=827712&admit=-682735245+1152513688084+28353475

interrupt the grub loader (hopefully you've got a pause there) by just hitting the arrow key around at the menu choice for the grub loader - this will make the timer countdown stop.

Then,
go to the line that holds your choice of the Linux load you want and hit "e" (for edit). This will bring you into an editor for the current load command. Choose the line you want ( I can't remember which one you need off the top of my head - there's probably two - try it on both), and hit "e" once again. Now, you should be editing a single line of the loader. Arrow key to the end of teh command and and the parameter "single" to the end of the line. Hit enter to "save" (only in the buffer - not on the disk) the command.
At this point - I think you hit "B" to boot it (read the screen).

System should boot into single user mode - needing no password. Change your password with the password command.

BTW, this is all a very good reason to lock your cabinet(s) for your servers and/or use bios password protection to boot the server, AND have a keypad lock on the server room...