Valve has added window mode functionality for DOTA 2. It allows players to run the game in windowed mode so they don’t have to switch windows (ALT-TAB) repeatedly to use messengers Skype, YouTube, WLM and other applications. It’s very useful when you’re streaming Dota 2 live games or writing a strategy guide.
How to play Dota 2 in Window Mode - Guide:
• Launch Steam client and login your account.
• Go the games Library, right-click Dota 2 and open properties.

• Then click, Set game Launch options. And enter “-windowed” command and click ‘OK’

• It will run the game in Windowed mode. But you need to set Width and Height to according to your needs.
• Add “-h #” and “-w #” command after “-windowed” to set your specific resolution, replace hash with the number of pixels.
• You may need to remove the borders and start-up video, Enter “-noborder” and “-novid” to remove it!