Xorg, choosing default resolution

[T <mlist4suntong@yahoo.com>]

Hi

My Xorg starts up in 1280x960 mode, which I don't like. I like it to be
1152x864.

How can I make my Xorg starts up in 1152x864 mode?

Here is my Screen. See, there is no 1280x960 listed in the mode, but yet
Xorg starts with it. 

Section "Screen"
	Identifier "aticonfig-Screen[0]"
	Device     "aticonfig-Device[0]"
	Monitor    "aticonfig-Monitor[0]"
	DefaultDepth     24
#	DefaultMode	1152x864
	SubSection "Display"
		Viewport   0 0
                Modes "1152x864" "1024x768" "800x600" "720x400" "640x480"
 		Depth     24
	EndSubSection
EndSection

The man page says "the first valid mode in this list will be the default
display mode for startup". Yet my xorg fails that also. Moreover, The word
"DefaultMode" is not recognized by Xorg.

So, how could I?

thanks

tong

ps 

- my xorg:

$ apt-cache policy xorg
xorg:
  Installed: 1:7.0.22
  Candidate: 1:7.0.22

- the same xorg.conf works fine for xorg6.9 before.