To disable Aero snap (Dragging windows off the edge get arranged into half of the screen):

Click on Start->Control Panel

Select the "Ease of Access center" category

Select  the option for option for "Change how your mouse works" under the "Ease of Access center" heading.

Towards the bottom of the page is the option "Prevent windows from being automatically arranged when moved to the edge of the screen" - Check this option and click "OK".

Now when you drag windows to the edge of the screen they will not be expanded to half screen size.