Well, you can set the default resolution through the xorg.conf in the "Screen" section under the "Display" subsection.
For example, here is a snippet of my xorg.conf:
Code:
Section "Screen"
Identifier "Screen0"
Device "LaptopScreen" #System-specific
Monitor "Generic"
# Compositing manager
Option "RenderAccel" "true"
Option "TripleBuffer" "true"
Option "DPMS" "true"
DefaultDepth 24
SubSection "Display"
Depth 24 #24-bits is the highest depth you can go. 32 Won't work
Modes "1280x700" #Here is where you specify the screen resolution
EndSubSection