How to specify primary monitor

[Che-Wei Chang]

How do I specify which monitor is  the primary monitor in Ubuntu 9.10?
I am using xorg driver for ATI RV250.
Following is my xorg.conf.


Section "Screen"
	Identifier	"Configured Screen Device"
	Device	"Configured Video Device"
	SubSection "Display"
		Virtual	2624 1200
	EndSubSection
EndSection

Section "Device"
	Identifier	"Configured Video Device"
	Option "Monitor-LVDS" "T42"
	Option "Monitor-DVI-0" "2007FP"
	Option "DisplayPriority" "HIGH"
	#Option "NoAccel" "TRUE"
EndSection

Section "Monitor"
	Identifier "2007FP"
	#Modeline "1600x1200"  160.96  1600 1704 1880 2160  1200 1201 1204
1242 -HSync +Vsync
	# Modeline    "1600x1200 at 60" 170.00 1600 1664 1856 2160 1200 1201
1204 1250  -HSync +Vsync
	# Modeline    "1600x1200" 130.25 1600 1648 1680 1760 1200 1203 1207 1235
	Modeline     "1600x1200_60.00" 139.800 1600 1640 1672 1864 1200 1201
1204 1250 +hsync +vsync
	Option      "dpms"
        Option      "DDCMode" "off"
	Option          "ReducedBlanking"
	HorizSync       30.0 - 81.0
	VertRefresh     56.0 - 76.0
	Option          "PreferredMode" "1600x1200_60.00"
EndSection


Section "Monitor"
	Identifier "T42"
EndSection