10.5.7 treats "HDMI" differently than 10.5.6 – Update Warning

Blog post by Brent Amersbach, MacMedics Baltimore:
We installed 10.5.7 on a MacMedics MacBook that we use as a media center tonight, and it made a wreck of things. We did see some on-line chatter about the topic, but that seemed to have something to do with attaching a Mac to any display via DVI to HDMI cables. Regular DVI, fine. VGA, fine. DVI to HDMI, PROBLEM! 10.5.7 now apparently treats “HDMI” differently than regular monitors, and by differently we mean completely different. It wants to use oddball resolutions that add in overscan rather than the regular native resolution of the panel. To make it worse, the native resolution tends to disappear as a choice in System Preferences.
You can turn overscan off, but then your display shrinks to a rectangle in the middle of the screen with a border around it, even if the resolution you’re using is greater than native. The only fix is to use this handy piece of third party software called SwitchResX that comes in a full blown shareware version, and a free control panel version. The free version seems to do the trick. It’s mildly complicated, so be prepared to re-configure it a few time to get it the way you want:
1. Launch the app
2. Tab over to Custom.
3. Hit the + button to bring up a dialog
4. Fill in what your display’s native resolution should be
5. Enable the Use Simplified Settings checkbox and choose one of the options from the newly enabled drop down menu to its immediate right
6. Click Apply and then reboot. See if the resolution now appears in Display Preferences
7. Repeat steps 5-6 until one of those drop down choices makes the custom resolution appear as an option.
If none of the three “simplified” choices work, you may be able to get it working by tweaking the settings manually, but this is for very advanced users only.
In short, if anyone has a Mac attached to a TV or even a regular monitor by HDMI, you may want to avoid 10.5.7 for the time being. See this Apple discussions thread for more details:
http://discussions.apple.com/thread.jspa?threadID=2004318&tstart=0