I want to setup dual monitor for the Dell Optiplex Gx520 computer.
The motherboard has an Intel Corporation 82915G Integrated Graphics
Controller.
Then I add an ATI Rage 128 video card.
The dual monitor work on Windows 2000 with the Intel chip as the
primary screen and the ATI chip as the secondary screen.
Therefore no problem with the hw.
However, dual monitor does not work on the Fedora core 6 (I can't use FC10).
The ATI chip is working but the Intel chip do not work (moving the
mouse do not go to that monitor and no image is displayed on the
monitor).

I configure dual monitor by using the "System, Display, Setting" menu
and clicking the "dual head" checkbox, then restart X server.
/etc/X11/xorg.conf is as follows:
# Xorg configuration created by system-config-display

Section "ServerLayout"
Identifier "Multihead layout"
Screen 0 "Screen0" LeftOf "Screen1"
Screen 1 "Screen1" 0 0
InputDevice "Keyboard0" "CoreKeyboard"
Option "Xinerama" "off"
Option "Clone" "on"
EndSection

Section "ServerFlags"
Option "AllowMouseOpenFail" "yes"
EndSection

Section "InputDevice"
Identifier "Keyboard0"
Driver "kbd"
Option "XkbModel" "pc105"
Option "XkbLayout" "us"
EndSection

Section "Monitor"

### Comment all HorizSync and VertSync values to use DDC:
### Comment all HorizSync and VertSync values to use DDC:
### Comment all HorizSync and VertSync values to use DDC:
Identifier "Monitor0"
ModelName "LCD Panel 1280x1024"
### Comment all HorizSync and VertSync values to use DDC:
HorizSync 31.5 - 67.0
VertRefresh 50.0 - 75.0
Option "dpms"
EndSection

Section "Monitor"

### Comment all HorizSync and VertSync values to use DDC:
Identifier "Monitor1"
VendorName "Monitor Vendor"
ModelName "LCD Panel 1280x1024"
### Comment all HorizSync and VertSync values to use DDC:
HorizSync 31.5 - 67.0
VertRefresh 50.0 - 75.0
Option "dpms"
EndSection

Section "Device"
Identifier "Videocard0"
Driver "r128"
EndSection

Section "Device"
Identifier "Videocard1"
Driver "vesa"
VendorName "Videocard Vendor"
BoardName "Intel Corporation 82915G Integrated Graphics Controller"
BusID "PCI:0:2:1"
Screen 1
EndSection

Section "Screen"
Identifier "Screen0"
Device "Videocard0"
Monitor "Monitor0"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 24
Modes "1400x1050" "1280x1024" "1280x960" "1280x800" "1152x864"
"1152x768" "1024x768" "800x600" "640x480"
EndSubSection
EndSection

Section "Screen"
Identifier "Screen1"
Device "Videocard1"
Monitor "Monitor1"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 24
Modes "1280x1024"
EndSubSection
EndSection

To try to setup dual monitor, then I modify /etc/X11/xorg.conf to
switch the Videocard0 & Videocard1 sections..
i.e.
Section "Device"
Identifier "Videocard0"
Driver "vesa"
VendorName "Videocard Vendor"
BoardName "Intel Corporation 82915G Integrated Graphics Controller"
BusID "PCI:0:2:1"
Screen 1
EndSection

Section "Device"
Identifier "Videocard1"
Driver "r128"
EndSection

I power down & up the computer but the same problem is still here -
the ATI chip is working but the Intel chip do not work.