resolution problem

[navygator]

hi all
excuse for my bad english
I have a little problem

I have a notebook asus m51kr with screen 15.4" WXGA and ati radeon 3470hd.
with windows optimal resolution is 1440x900 but with linux kubuntu/itrepid maximum resolution is 1280x800. I edit xorg.conf, I use aticonfig --resolution, but resolution 1440x900 not added.
I use ati catalist 8.12 first and now 9.1 beta

I post my xorg.conf

Section "ServerLayout"
	Identifier     "aticonfig Layout"
	Screen      0  "aticonfig-Screen[0]-0" 0 0
EndSection

Section "Files"
EndSection

Section "Module"
EndSection

Section "ServerFlags"
	Option	    "Xinerama" "on"
EndSection

Section "Monitor"
	Identifier   "aticonfig-Monitor[0]-0"
	Option	    "VendorName" "ATI Proprietary Driver"
	Option	    "ModelName" "Generic Autodetecting Monitor"
	Option	    "DPMS" "true"
EndSection

Section "Device"
	Identifier  "aticonfig-Device[0]-0"
	Driver      "fglrx"
	Option	    "UseFastTLS" "1"
	BusID       "PCI:1:0:0"
EndSection

Section "Screen"
	Identifier "aticonfig-Screen[0]-0"
	Device     "aticonfig-Device[0]-0"
	Monitor    "aticonfig-Monitor[0]-0"
	DefaultDepth     24
	SubSection "Display"
		Viewport   0 0
		Depth     24
		Modes    "1440x900"
	EndSubSection
EndSection

thanks all

[RealNC]

Try xinerama off.

[navygator]

i tried xinerama off, problem remains

[navygator]

I not resolve problem. any idea?