Disable Fullscreen

[Xilef]

How do I disable the full screen (Alt + Return) in game? I want people to be able to see the Close Window button in Battle World, but they can't if it's in Fullscreen, that and the FMV's wont work in full screen, so how would I disable the option of full screen?
(An idea would be to ask if the game is in fullscreen and if it is return to window mode)
So can someone tell me the code snippet I need?

 

[Xilef]

This is perfect! Thanks! It works just the way I imagined it and there are no errors or bugs. Thanks!