I'm running Ubuntu 9.10 on Acer Timeline 4810G and I have installed ATI driver.

I tried to connect my Samsung 1680*1050 T220N as an external display. When I open System-Preferences-Display I see my external monitor, but I'm unable to set resolution higher than 1366*788, and when I click apply it asks me to logout and login again for settings to take effect. And my external display remains black.

When I used the intel adapter all worked OK.