Honestly, I'm not sure if what I tell you know will work. But Magic is on Vacation right now, so I cannot doublecheck.
First, the GUI hasn't been up yet (because it will need new graphic) The new resolution will only show ingame in a mission.
Here is what I did to get my 1920 x 1080 working :
1) open the file "prefs.cfg", located in the main folder of MCO.
2) In the botton, you see the four available resolutions from retail.
3) Change the value from 1280x1024 to what you like.
4) Ingame, set the option to 1280x1024 ( what the spaces, type : 3 = 1280by1024)
5) In a mission, you will now have the resolution of your choice.
I'm not sure if this is the correct way or just a hack, but it works. Magic will be back at the end of june, he can say better
