--save this script to ~/Library/Scripts/Applications/TextMate/
--you'll need to have "Enable access for assisstive devices" enabled under Universal Access in System Preferences

set {screenWidth, screenHeight} to {1280, 854} --set your screen resolution here
set menubarHeight to 22

tell application "System Events"
	tell application process named "TextMate"
		set bounds of window 1 of application "TextMate" to {0, menubarHeight, (screenWidth / 2), screenHeight}
		set bounds of window 2 of application "TextMate" to {(screenWidth / 2), menubarHeight, screenWidth, screenHeight}
	end tell
end tell