I haven't read through this thread, so I don't know if it's already been covered, but if you want OS updates to work without waiting for hacked versions, install the Vanilla Kernel.
no, even with a vanilla kernel going through apple su will break it. however not the case for 10.5.4 as they didnt change system kexts
you still have to run commands via terminal with the update file or wait for a hacked version
source: from my own unlucky experience lol