Under Gutsy, this will work (may be easier/better ways to do this):
- run command 'nvidia-settings' and go to 'X Server Display Configuration'
- If you are all plugged in, there should be two grey boxes displayed, one labeled 'LGP' (your LCD screen) and another (mine's labeled 'LG').
- Change the resolution of your current display to match what you will be using (most projectors are 1024x768)
- Now, click on the LG box. (The way to control which display you are dealing with are clicking and moving those boxes)
- You should see a box with a Configuration: Disabled and button [Configure]; click the Configure button.
- How Should this display device be configured? Click 'TwinView'
- Resolution 'Auto'
- Position 'Clones'
- Then hit 'Apply'
If you want to run this configuration with no setup, then click on the 'Save to X Configuration File' and copy it over your /etc/X11/xorg.conf file whenever you need it (make sure you backup your original xorg.conf file!)
To undo it, click on the Configure button for LG, and click 'Disabled'. Then, change the resolution for your current screen and hit the 'Apply' button.
NOTE: this does not want to work under wmii-ruby because it does not want to respond to the change in resolution from gnome-display-properties.