If you can boot with a live distro like knoppix, then you could mount the partition and access the files directly (and copy them to an external drive) without having to log in. ( provided that the partition isn't encrypted ) You don't need to reset the password.
The process of resetting a password is to edit /etc/shadow and delete the characters between the first and second ":" character.
- sudo /sbin/fdisk -l
- sudo mount -t ext31 /dev/sda5 /mnt
- sudo vim2 /etc/fstab
- <edit out the encrypted password hash>
- reboot the computer and login without a password
The filesystem may be different. Use the output of fdisk -l to determine it. ( the -t ext3 part )
You can use any editor, you don't need to use vim.