So when I play in Windowed or Borderless mode, I can't alt tab to any other program. I can't check my browser, the League client (not the game, rather the actual client with whispers and chats), Skype, or anything else.
The problem is, if I go into full screen mode the game won't stream. I'm trying to become a streamer/caster and I need to be able to check my streaming programs, Skype and everything else for any technical problems and criticisms during the matches I'm casting. What do?

Try using Aero for that

Windows Key+Tab

Borderlands mode?

dont work. you'd need a third party like shiftwindow

I can alt tab fine on Win7. If you are using Vista, that is why.

Can your mouse leave the confines of the window when you open the menu?

Drasthian,

When you first go to Borderless mode you may not be able to alt-tab properly.

To get around this. Launch a game (try a custom game with only you in it so you don't have to actually play the whole thing). Set the game to Borderless mode.

Exit the game completely. And then launch a new match This time you'll start off in Borderless mode and should now be able to Alt-Tab properly.

Still having an issue?

Your best bet is to contact one of our Tech Specialists here: https://support.leagueoflegends.com/home

So, I restarted the client this time in borderless (I switched from full screen to borderless, closed, then restarted the LoL client) and now it works. Odd glitch involving switching from full screen to borderless maybe?

EDIT: Shen'd by the Cookie Eagle Wookie thing. Thanks, I did this exactly and now it works.

Mad upvotes for ~5min red response time.

(Guess you guys really are listening... can we have ranked Dominion soon?)