Seemingly unsolvable viewmode weirdness?

Time and time again when I’m working in Blender I manage to accidentally hit some button which causes two of my three windows and all the buttons on the menu below to disappear. After this it seems impossible to split the window I have open to re-make the lost windows as the cursor doesn’t form a double arrow when it touches the edges.

I’m guessing this is some kind of “put window in full-screen” mode, but I am at a loss when it comes to restore “normal” view, does anyone knows how to do this?

(I’m using 2.49b if that makes any diff.)

Ctrl+up arrow toggles full screen mode