Windows 7 provides a new feature which
is called “Aero Snap”. You can minimize, maximize, resize window by
just dragging-dropping it to the screen corners.

You can prevent windows from being automatically arranged when moved to the edge of the screen by following these simple steps.

• Open Control Panel by using Start Menu.
  
• Select Ease of Access Center,
  
• Select Change how your mouse works or Make the mouse easier to use option.
  
• Now, under Make it easier to manage windows, activate the option button described on the image below, and click on OK.
  

Source : WinSpark.net