Haven't read through the entire thread yet, but just wanted to note that, under Vista x64, this does not work for me. When I update the driver and point it to the dir with the gxm.inf, it simply says:
Windows has determined the driver software for your device is up to date.
Generic PnP Monitor
**DANGER DANGER WILL ROBINSON CROSSPOST AHEAD**
OK.... here we go... "thankfully you all have a talented and gifted security agent..."
If your monitor is listed as Plug and Play, it needs to say Matrox TripleHead2Go Edition, if not the games will not run in 5040x1050. This is of course assuming your desktop is currently at 5040x1050.
Right click on the monitor list (i.e. Plug and Play Monitor)
Properties
Driver
Update Driver
Browse my computer for driver software
Let me pick from a list of device drivers on my computer
have disk
browse (to your PowerDesk install directory, usually c:Program Files (x86)Matrox Graphics IncPowerDesk SE)
Highlight GXM.inf
Open
**you may get a pop up asking if you want to Trust Matrox, if so say yes**
This should install the correct monitor listing and allow you to play games in 5040x1050. I just checked COD4 and X3 (my two favorites) and I now have the option.
I hope this helps out the other people having issues.
**EDIT**
I now have the following resolutions listed in the SGU
4098x768
4320x900
5040x1050