If OpenGL is off, it could be causing that \"lag\" (actually a low framerate). Slower comps software render slower.....much slower. Not much of a problem if your comp is above 2ghz, but for a PIII 833mhz you pretty well have to rely on your hardware(3D card and ram).
Good luck solving your next problem - oh, and I\'d keep your monitor on 16bit. It doesn\'t slow your computer down nearly as much.