no 1920x1200 option available

Are you saying that 1920 x 1200 is not showing up as a choice within Displays Preferences on the mini, or are you saying that when you select 1920 x 1200 on the mini, you don't get a screen (black screen)?

Also, what generation mini is it? A G4 or Intel? And how are the two cabled together, VGA or DVI?

Try the following to see if it fixes the issue:

Go into Displays Preferences and put a check mark in the box for "Show displays in menu bar".
Under the resulting icon (looks like an old Apple Cinema Display) in the menu bar, drop down the menu and select "Number of Recent Items" and set it to 10.
Now drop the menu a second time and see if 1920 x 1200 shows up as one of the 10 choices.

If the above procedure doesn't work, you may be a victim of the widespread trouble that several users are reporting after having updated to 10.5.7. You could try downloading the combo updater and running it again to see if that fixes it. Here is a link to the combo updater:

http://support.apple.com/downloads/MacOS_X_10_5_7_ComboUpdate

If that doesn't work, several people have had success using SwitchRes X to restore missing resolutions:

http://www.madrau.com

Thanks for this - however SwitchRes did not help me restore 1360x768 I had prior to 10.5.7 update. I'm using a Mac mini and 32" Samsung LA32R81BD.

I tried using the SwitchRes common tab, as well as defining a custom res based on specs in the manual. Neither added the required res to my SwitchRes active list after a reboot.

when i upgraded to 10.5.7. which i already did before from 10.5.6. and my native resolution dissapeared (native: 1920x1200 but only 1920x1080 was avaiable) so i went back to 10.5.6.

i realized that if i uncheck overscan option under 10.5.6. than it would make the native resolution also disappear, but i could restore it with rotating the screen 90' but not confirming it, i let osx to revert back to normal position and the native resolution option came back. now i wonder wether i could use it after 10.5.7 when native resolution had dissapeared by default.

any experience with this?