xorg.conf is located at /etc/X11/xorg.conf.
Mine looks like this:
Code:
#
# X.Org server configuration file generated by Parallels Guest Tools.
#
# Parallels Video section
Section "Device"
Identifier "Parallels Video"
Driver "prlvideo"
EndSection
# Parallels Monitor section
Section "Monitor"
Identifier "Parallels Monitor"
VendorName "Parallels Inc."
ModelName "Parallels Monitor"
EndSection
# Parallels Screen section
Section "Screen"
Identifier "Parallels Screen"
Device "Parallels Video"
Monitor "Parallels Monitor"
Option "NoMTRR"
SubSection "Display"
Depth 24
Modes "1920x1080"
EndSubSection
EndSection
# DefaultFlags section
Section "ServerFlags"
Option "AllowEmptyInput" "yes"
Option "AutoAddDevices" "yes"
EndSection
# DefaultLayout section
Section "ServerLayout"
Identifier "DefaultLayout"
Screen "Parallels Screen"
EndSection
The part you're interested in is Section "Screen", SubSection "Display", line "Modes". Put your desired resolution on that line. Mine, as you can see, is 1920x1080. Save the file, log out, log back in and see if that helps.