Well, I installed 10.5.7 on one of my Mini 9's and it is freezing. I get the gray screen with the Apple logo, then the spinning gear wheel. Gets to a blue screen then goes gray again with some broken bands of lines. If I hit "Fn + 8" the screen then goes to the startup Apple logo with a frozen gear wheel and freezes.
I rebooted and tapped the spacebar on "Press any key to enter startup options"
at the boot prompt I type "-v" (minus quotes of course) and then hit ENTER. This looks to be a diagnostic mode (never ran it 'till now) where a bunch of commands scroll by. Simmilar results as with first step but instead of a gray screen with broken up lines, I get a black background with the white text all garbled up. I then hit "Fn + 8" and the screen is cleared up.
Here are the last two lines at the bottom of my screen before the system freezes:
May 13:01:07:34 localhost /usr/sbin/ocspd[66]: starting
May 13:01:07:34 localhost mDNSResponder mDNSResponder-176.3 (Sep 30 2008 16:59:38)[34]: starting
This is where it all freezes. Hope someone can use this to diagnose! Oh well, it's time to reload unless there is a recovery mode where one can undo the previous update, ala Windows?