Otherwise, boot into single user mode and change the password...
another option, use a recovery CD/Disk. Boot using this. Mount the filesystem that /etc resides. Edit the /etc/shadow file with a generated passwd from an alternate machine. umount the filesystem, reboot and voila you should have root with a new password.
In many cases, when you don't have a user with su ability, and you're no where near the physical machine, you're going to have to get the data centre to do this for you. In the end, it's a pretty important word to forget and it's not supposed to be trivial to reset.