I got a new imac that came with 10.7 on it. We have an older system that requires a client that runs in powerpc mode so I needed to downgrade to 10.6. Easy right? Just put in the 10.6 retail DVD and boot to it and install – right? NOPE – Nothing is ever easy.
Here's how I made it work:
- Put the target computer (the one you want to downgrade) in target disk mode (hold t when booting).
- Boot the 10.6 install DVD in a computer that allows you to boot to it. (Make sure the firewire is plugged into this mac).
- I got an error "Mac OS X cannot startup from this disk." and found you have to re-partition the firewire drive as a GUID partition.
- Then you can install 10.6 like normal on the firewire disk.
- Run all the updates and once you're fully updated then shut it down and boot the new mac like normal into 10.6!
*Update: Be carefull, Macs with Intel HD Graphics 3000 are not supported in 10.6.