I haven't tried this information yet, but I found it on a forum and thought it was useful to keep...

Reseting a system you have lost the password to.


assuming you are using the grub bootloader

select the option to boot as normal but instead of pressing enter press e
add init=/bin/sh to the end of the kernel line
select the boot option, the system will start to boot but then early in the boot process will drop you to a shell

at the shell do

mount -o remount,rw /
passwd root
<enter a new root password>
init 3

the system should now boot to the login prompt allowing you to log in as root using the password you set above.