Here is the Frame Buffer mode:
mode “1152×768-55″
#D : 64.994 Mhz, H: 44.154 kHz, V: 54,701 Hz
geometry 1152 768 1152 768 8
timings 15386 168 26 29 3 136 6
endmode
In Ubuntu Gutsy, by default the frame buffer is 640×480-60, just type this in a tty and restart your gdm (or equivalent), to have full screen.