How do I reset the root password if I've forgotten it?

Pretty simple (if you have physical access to the machine). Reboot the machine with a boot/rescue disc. Mount your linux partition and go change the password in /etc/passwd or /etc/shadow (as appropriate) to nothing. Reboot, login as root, (no password), then: passwd to change your password. Try to remember it this time!

If you don't have physical access, I guess you don't own the machine so it is none of your business to know the root password anyway. If the machine you own is merely hard to get to (like 3 hours drive), then you will either have to make other arrangements with people closer, or go for a long drive.