Try hitting the windows key instead of or in combination with Alt+Tab. I find that as others have said, the game will only switch if there is something available to switch to, the start menu does this.
As for true windowed mode, I cannot say.
However I have noticed that if I alt+tab from EB and then back again, after fighting a battle I usually get a CTD. Could just be me though but worth bearing in mind if you start experiencing crashes.
Cheers