Some people (including me) have lost the ability to select a resolution of 1152x864 in certain circumstances. This seems to have disappeared during various generations of Panther updates. There is also some speculation on the web about Iiyama monitors not reporting all the available resolutions.
On one of my systems that has had Panther installed from scratch, 1152x864 is not an optional resolution, and it does have an Iiyama monitor connected. On a 19" monitor, this size is a good compromise between text size and desktop space. One solution is to use a shareware app to add to available resolutions -- there are several out there -- but quite honestly, I just wanted to add it and forget it.
After extensive testing, the only thing that is needed to get 1152x864 back is to add one line to a file named IOGraphicsProperties.plist. This file is located in /System -> Library -> Frameworks -> IOKit.framework -> Version -> A -> Resources/.
Naturally, you have to be logged in as root to get at this file. All the usual stuff applies -- make a copy of the file, save it safely somewhere, and edit the original in TextEdit). Near the top of the file, look for the line that reads:
<key>gtf-resolutions</key>
Below this line is a list of resolutions. Add the following line after the one with 1024 in it:
<integer>1152</integer>
I have found that it is not necessary to change any of the resolution lists that follow this array. Save the file, quit the editor, and reboot. You should now have 1152x864 as an option in Display preferences. Presumably the aspect ratio is calculated from the 1152, as it was not necessary to change anything else.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050220090150361