UPDATE:
I have tried hooking into the Gens emulator window and changing the max size using WM_GETMINMAXINFO, but this didn't seem to work (see knowledge base article Q185733) . I can hook into a VB form and control its maximum size this way, but it doesn't work for the emulator window. I can manipulate the emulator window in other ways (moving it, resizing it, though not larger than the screen resolution )using API calls, so I know I have the correct window handle, but I can't seem affect its maximum size this way.
Argh! Searching the web and newsgroups hasn't turned up any solutions.