Screen and projector resolution

[Dimitrios Eftaxiopoulos <eftaxiop@central.ntua.gr>]

Hello,
I have a laptop computer equipped with a NVIDIA GeForce 9800M GTX graphics 
card. The screen works with the default 1900x1200 resolution. I tried to lower 
down this resolution e.g. to 1900x1120, so that the latter coincides with the 
resolution of the projector which I use for presentations. Otherwise, part of 
the computer screen does not appear on the overhead projection. However, the 
only option available in the NVIDIA Settings Tool for the computer screen is 
1900x1200. My xorg.conf file contains the following

Section "Device"
        Identifier      "Configured Video Device"
        Driver          "nvidia"
EndSection

I added more, lower resolutions in the xorg.conf file, at no success. 
No other resolution options are available in the Kickoff --> Setttings --> 
Screen menu of KDE, as well.
I use unstable/amd64, 2.6.30-2 kernel, kde 4.3.2.

Any help is appreciated
Dimitris