Surely its easy to simply resize the mirc window to the resolution you want? changing resolution colour depth and monitor refresh frequency seem a little drastic, computers allow 320x240 still? sure its possible but i thought windows xp's minimum was 800x600 (albeit games do what they like). that said im sure there's nothing worse than a broken mirc for dos? or whatever ancient script it sounds like are using. if it is pretty old, archaeologists might be interested as it sounds like some kinda of rare artifact.
My ramblings aside.... right click the desktop, settings. change the resolution?