Erg.. I know there is a way to do it. I have a monitor at 1366x786, on Ubuntu, trying to configure a Windows XP instance on Qemu to that exact same size..
All of my searching with xorg has said I need to configure xorg.conf to get Qemu to do full screen. Although it doesn't specify the minimum configuration requirements. Also I've never configured xorg by hand, so I wouldn't know how to start from that angle.
Any help on which direction to go would be awesome..