i did this and nothing changed - still got stopped with the "boot0: MBR / boot0: error" message.
stick your OS X disc in the drive and press f8 on command and then boot with -s flag (so at prompt it should be boot:-s) and boot into single user mode then issue the command:
fdisk -u /dev/rdisk0
and follow the prompts. now the darwin bootloader will be on the mbr and osx will be the default os
i've attached the list of my drives as shown in the disk utility. i boot off of "the big lebowski". all partitions and external drives are Mac OS Extended (Journaled). i'm running ideneb 1.3 / leopard 10.5.5 and there are no other issues once booted up.
i should note - i just checked into the 'startup' disk options and my OS X install doesn't appear under the options. the install cd and Network Startup do, but not any of my hard drives.