I get this:

(WW) I810: No matching Device section for instance (BusID PCI:0:2:0)
found
(EE) No devices detected.

I added Videocard1 in addition to Videocard0 that was already there
and BusID into both sections but apparently that's not enough.
Section "ServerLayout"
Identifier "Default Layout"
Screen 0 "Screen0" 0 0
InputDevice "Keyboard0" "CoreKeyboard"
InputDevice "Synaptics" "CorePointer"
EndSection

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

Section "InputDevice"
....
EndSection

Section "Device"
Identifier "Videocard0"
Driver "i810"
BusID "PCI:0:2:1"
EndSection

Section "Device"
Identifier "Videocard1"
Driver "i810"
BusID "PCI:0:2:0"
EndSection

Section "Screen"
Identifier "Screen0"
Device "Videocard0"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 24
EndSubSection
EndSection

Section "Screen"
Identifier "Screen1"
Device "Videocard1"
DefaultDepth 24
SubSection "Display"
Viewport 0 0
Depth 24
EndSubSection
EndSection

from lspci on that FC6 box:
00:02.0 VGA compatible controller: Intel Corporation Mobile 945GM/GMS/
940GML Exp
ress Integrated Graphics Controller (rev 03)
00:02.1 Display controller: Intel Corporation Mobile 945GM/GMS/940GML
Express In
tegrated Graphics Controller (rev 03)