The portion you're looking for is...
Code:
SubSection "Display"
Viewport 0 0
Depth 16
Modes "1280x768" "800x600" "640x480"
EndSubSection
SubSection "Display"
Viewport 0 0
Depth 24
Modes "1280x768" "800x600" "640x480"
EndSubSection
EndSection
Where it says...
Code:
Modes "1280x768" "800x600" "640x480"
you need to add "1024x768". So it should look like...
Code:
Modes "1280x768" "1024x768" "800x600" "640x480"