Password Reset Disk

Actually, there's no need for a separate disk, you just boot into recovery mode and do it from there.

If you don't see grub at boot time then hold down the shift key as the machine starts, and the text-based menu should pop up before the ubuntu logo. If you do see grub (if you have a dual-boot setup you normally will) then ignore this step.
Select the top-most 'Recovery mode' option. The machine will boot to a coloured text-mode 'Recovery Menu'.
Select 'remount'. Hit enter when it's done.
Select 'root'.
Set the password with passwd <username>.
reboot

Seems insecure right? This is why you should encrypt your user account if you care that much.

This can usually be done from the live cd. All you have to do is boot from the live cd and run these commands, adjusting for your system:

sudo mkdir /mnt/ubuntu
sudo mount /dev/sdXY /mnt/ubuntu
sudo chroot /mnt/ubuntu
passwd <insert-username>
exit
sudo umount /mnt/ubuntu

Now reboot into your installed system and your password will be changed to what you entered in the passwd command's prompts.

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