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?