From my limited knowledge on the subject (someone please verify or contradict this), full screen games or other programs with a true full screen mode (this is not the same as a maximized window) create problems when determining desktop resolution. Part of this is likely due to how such programs/games allow a different resolution than what you have as your desktop resolution, though there may be some other reason. I think that if you were to try and display the screen height and width on a timer and then open a game, you'll find that the results drop to either 0 or 1 until you minimize or close the game. This is likely the reason the window isn't centered -- it's trying to center at 0,0. I'm not certain if this is a Windows issue or a mIRC issue, but I have seen it before in mIRC.
