Change OS Window Size

I found out how to change the resolution inside the game window to 1024x768, but I also want to change window (as in the Window running as an application in WinXP) to be 1024x768 - right not it is just around 800x600.

Is there a command to change the size of the window, or a place (prefs file, etc.) where I can change this?

Thanks,

Jeremy