When playing a non-joystick game such as "Realms of Chaos", while I am beating away at the Ctrl and Alt keys I sometimes accidentally press the windows key and the screen resolution changes from full screen down to a small window. Is there a way of changing back to the full window without killing the game and starting from the beginning?

Alt+Enter ?
Sounds like you're hitting the Windows key.

^This

If you have a joystick, you can use software like JoyToKey to play old DOS games with it. That might be a little easier to play with.