currently my labtop monitor is cracked and only able to view some screen on my labtop, its a sony vaio VGN-CR32, so I went out and bought a ACER 22 inch flat monitor to help me at least still use my labtop. Anyways I'm having problems trying to get the right screen resolution to work out. At least on my labtop I was using 800 by 600 and 75Hz refresh rate, of course by the time I hook it up to my computer monitor basically everything gets bigger and have no way of keeping a small area like I had before, I can no longer mininize or maximize firefox i just have to quit. Trying to use my screen to virtualbox is unable since the screen become to big. Anyway to fix this problem. I am on ubuntu 8.10

Are there any Fn + [key] combinations that you can use to disable the laptop's built in monitor?

Maybe try that and then reboot from the install CD with the external monitor attached to force Ubuntu to reconfigure the X server for the external monitor and then copy the settings back over to the Ubuntu installation?

I don't know where Ubuntu etc store the xorg.conf settings, but google should be able to help.