You are using vesa driver for some reason. Change it to ati, and remove the Monitorlayout-option. Also, add "1680x1050" to the list of modes (before 1280x1024).
Did you upgrade from Edgy? -- xserver-xorg-video-ati broken in Feisty https://launchpad.net/bugs/98800 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
