Joe van Tunen - 2011-11-07

Your broken hard disk should not affect being able to boot from system DVD. Insert the DVD and hold the option key at startup and select the DVD to boot it. Or hold the C key at startup. If you can't boot from the DVD, then the DVD is broken or is not meant for your Mac.

The partition information is stored in 3 locations: the MBR (block 1), the primary GPT (block 1 - 33), and the secondary GPT (last 33 blocks).

"gpt fdisk" can be used to examine those. If any of them contain valid information, they can be used to repair the others. You'll need to make some decisions if they contain conflicting information.