1400x1050 on Intel 915GM
If your laptop panel has an unusual native resolution such as 1400x1050, and the native resolution is not automatically supported, you may need to download and install the program 915resolution, read the documentation and add a line into /etc/rc.local such as:
915resolution 3c 1400 1050
and then configure /etc/X11/xorg.conf with care... see x.org FAQVideoModes.
Hint:
Restart X without an external monitor attached, or use an external monitor having the same or higher resolution than the laptop panel. As of xorg 7.0, the external monitor is probed for its limits and xorg will refuse to allow the internal LCD to be driven at resolutions higher than the external monitor will allow.