# VirtualBox generated configuration file
# based on /etc/X11/xorg.conf.

Section "Monitor"
 Identifier   "Monitor[0]"
 ModelName    "VirtualBox Virtual Output"
 VendorName   "Oracle Corporation"
EndSection

Section "Device"
 BoardName    "VirtualBox Graphics"
 Driver       "vboxvideo"
 Identifier   "Device[0]"
 VendorName   "Oracle Corporation"
EndSection

Section "Screen"
 SubSection "Display"
 Depth      24
 EndSubSection
 Device       "Device[0]"
 Identifier   "Screen[0]"
 Monitor      "Monitor[0]"
EndSection
Nun ergänzen Sie folgende Zeile unter SubSection “Display”:

Modes "1280x1024" "1152x864" "1024x768" "800x600" "640x480"