Can't make Matrox G550 dual-head work

We have a dual-head Matrox 550 on a fresh install of FC1. It's set the monitors up in some fashion (there's an entry for each in XF86Config), and there's an 'Option "Xinerama" "on"' in there [and 'Option "Clone" "off"], but the only thing I can make it do is have one single screen cloned on both monitors.

I've googled around and found a couple of example 'XF86Config's [one with two of screen/device/monitor, one with a single 'merged' screen] and niether seem to make any diff.

  The card worked fine under Win2000 before we wiped that to put on Fedora.

Any pointers or other examples? Here's what the installer put in the XF86Config:

# XFree86 4 configuration created by redhat-config-xfree86

Section "ServerLayout"
        Identifier     "Multihead layout"
        Screen      0  "Screen0" LeftOf "Screen1"
        Screen      1  "Screen1" 0 0
        InputDevice    "Mouse0" "CorePointer"
        InputDevice    "Keyboard0" "CoreKeyboard"
        InputDevice    "DevInputMice" "AlwaysCore"
        Option      "Xinerama" "on"
        Option      "Clone" "off"
EndSection

<snip>

Section "Monitor"
        Identifier   "Monitor0"
        VendorName   "Monitor Vendor"
        ModelName    "Iiyama S902JT, VisionMaster Pro 451"
        DisplaySize  360        270
        HorizSync    27.0 - 115.0
        VertRefresh  50.0 - 160.0
        Option      "dpms"
EndSection

Section "Monitor"
        Identifier   "Monitor1"
        VendorName   "Monitor Vendor"
        ModelName    "Iiyama A701GT, VisionMasterPro 400"
        HorizSync    27.0 - 96.0
        VertRefresh  50.0 - 160.0
        Option      "dpms"
EndSection

Section "Device"
        Identifier  "Videocard0"
        Driver      "mga"
        VendorName  "Videocard vendor"
        BoardName   "Matrox Millennium G550"
EndSection

Section "Device"
        Identifier  "Videocard1"
        Driver      "mga"
        VendorName  "Videocard Vendor"
        BoardName   "Matrox Millennium G550"
        BusID       "PCI:1:0:0"
EndSection

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

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

--
[neil@fnx ~]# rm -f .signature
[neil@fnx ~]# ls -l .signature
ls: .signature: No such file or directory
[neil@fnx ~]# exit