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User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20050922 CentOS/1.7.12-1.4.1.centos4

Description of problem:
I want to use my laptop with a data projector, plug it into the back of the machine, see my presentation on the laptop screen as the audience view the same thing from the projector. This used to work, then sometimes did/didn't but became less & less. I assumed something like incompatability between laptop & projector.

Recently I could not get it to work and someone suggested that I set the laptop as dual head ... I then got another desktop displayed by the projector, but different from the one on the laptop screen. This shows me that there is no incompatibility. What I want it to have the same desktop & applications displayed on both - so that the audience can see what I am seeing.

Version-Release number of selected component (if applicable):
xorg-x11-6.8.2-37.FC4.49.2

How reproducible:
Sometimes

Steps to Reproduce:
1.Plug in data projector to back of laptop
2.Not see anything on the data projector
3.
  

Expected Results:  The same on the laptop screen as the data projector.

Additional info:

part of: /etc/X11/xorg.conf
Section "Monitor"
        Identifier   "Monitor0"
        VendorName   "Monitor Vendor"
        ModelName    "LCD Panel 1024x768"
        HorizSync    31.5 - 48.5
        VertRefresh  40.0 - 70.0
        Option      "dpms"
EndSection

Section "Device"
        Identifier  "Videocard0"
        Driver      "sis"
        VendorName  "Videocard vendor"
        BoardName   "SiS 630/730"
EndSection

lspci tells me:
01:00.0 VGA compatible controller: Silicon Integrated Systems [SiS] 630/730 PCI/AGP VGA Display Adapter (rev 31)