Possible Duplicate:
Windows 7 resize shortcuts to Mac OS X
In Windows 7, if I drag a window to the far right or left of the screen, it will resize and reposition the window to take up half of the screen on that side. It will also maximize the window if I drag it to the very top of the screen. Is there any way to accomplish similar behavior in Mac OS X, either built into the OS itself or via some downloadable extension?