Ubuntu 9.10 does not use xorg.config for display settings. I’m running a VirtualBox in a Vista Laptop to host Ubuntu 9.10. The laptop supports a native 1680×1050 resolution and I like to use my Ubuntu in full screen mode with full native resolution. As VirtualBox provides only a virtual display, not the nVidia card from the laptop.

Here’re the steps to enable more resolutions:

1. Make sure you have installed guest additions in Ubuntu
2. run the command “cvt 1680 1050” and copy the output to the next command
3. sudo xrandr —newmode “1680×1050_60.00” 146.25 1680 1784 1960 2240 1050 1053 1059 1089 -hsync +vsync
4. sudo xrandr —addmode VBOX1 1680×1050_60.00
5. sudo xrandr —output VBOX1—mode 1680×1050_60.00

You can add more resolution with above steps. The new resolution modes will be available in Display preferences too.

I saved the steps 3-5 into a file disp so it could be used next time.