Trebaš kao root editirati xorg.conf fajl.naći ćeš ga u /etc/X11...ovo je dio koji je tebi bitan:
Section "Screen"
# If your card can handle it, a higher default color depth (like 24 or 32)
# is highly recommended.
# DefaultDepth 8
# DefaultDepth 16
# DefaultDepth 32
# "1024x768" is also a conservative usable default resolution. If you
# have a better monitor, feel free to try resolutions such as
# "1152x864", "1280x1024", "1600x1200", and "1800x1400" (or whatever your
# card/monitor can produce)
Identifier "Screen 1"
Device "Inno3D Geforce 2 MX400"
Monitor "Samsung 730BF"
DefaultDepth 24
Option "nologo" "1"
#VideoRam 4096
SubSection "Display"
Depth 8
Modes "1280x1024" "1280x960" "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 16
Modes "1280x1024" "1280x960" "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 24
Modes "1280x1024" "1280x960" "1024x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Depth 32
Modes "1280x1024" "1280x960" "1024x768" "800x600" "640x480"
EndSubSection
EndSection
Kod tebe vjerojatno nije baš tako,ali u principu dodaš samo reze koje trebaš.Restartaš X i to je to.