I have a MacBook Pro running 10.5.8.
I have an external USB drive, partitioned, GUID.
I have cloned a Leopard install DVD to one partition 1 (8.5Gb).
I used that to install Leopard to Partition 2 (30Gb)
Booted from Partition 2 - boots fine.
Used Software Update to upgrade to 10.5.8 - update proceeded normally.
Partition 2 will no longer boot - grey screen with big apple at centre - daisy wheel spins forever.
Next time I installed to Partition 2 with the Leopard DVD.
Booted from partition 2.
Used a downloaded 10.5.8 combo updater.
Mac since 1984, Apple since 1978
MacBook Pro, iPhone 5, MacBook (in living room for iTunes and searching for recipes), iPad