Mac Hardisk not Booting - partition map

Apple iMac (Mac OS X 10.4) is not booting.

1. Start iMac and press "T"
Connect by firewire cable to another Mac Computer (Mac OS 10.7).
Start "Disk utility" program.

"First Aid"
"Verify Disk"
"Repair Disk"

Error was found
"Problems were found with the partition map witch might prevent booting."

In my case the "First Aid" could not help.

2. I tried to boot the iMac with Disk Warrior (v.4).
But the repair program could not repair the hard disk.

3. I installed the Windows program "MacDrive" on PC Windows XP.
(5 day free test program)
Connect my Mac Harddisk to windows, with USB external hard disk device.
But MacDrive found error on harddisk and could not repair.

4. Found blog from "Broes"
http://www.broes.nl/2008/01/restore-an-apple-partition-map/
I installed "TestDisk" on Mac (10.7).
Connect the hard disk with USB external hard disk device.
Tried to understand the program.
The program could not see the rotten hard disk.

5. Idea to use TestDrive on Windows Computer.
Connect the rotten hard disk by USB external device to Windows PC.
Suddenly the rotten Mac Hard disk is mapped.
I could copy all the data to another external hard disk.

Summary: I could not really understand the "repair" of the hard disk.