Another Key Command question: Alt-F4

On my Mac Pro Alt-F4 serves to quit PC applications and also to Turn Off Computer

On my MacBook it launches Spaces!

Can anyone suggest:

how to implement Alt-F4 so it quits applications

how to disable Alt-F4 from launching Exposé and Spaces prefs - even though I have spaces disabled?
Alt-F4 is not listed in OSX keyboard&mouse shortcuts AFAICT

peter

 

question closed

If I use the 'fn' key on my macbook, fn-ALT-F4 does the trick

issue closed

peter