If you happen to be using a Darwin boot CD to install Leopard on a PC, and happen to render your system unbootable, you can mount the system partition using a single command:
mount_hfs /dev/rdisk0s2 /mnt
where '0' is the disk number, '2' is the partition number, and '/mnt' is the folder where the files in that partition will appear.
Hope this helps! It helped me. I got it from here.