In Windows 7, there's a window auto snap feature called Aero Snap. When you drag a window to any edge of the screen, it automatically snap and resize the window. Also, holding the ❖ Win key then press any of the arrow key also works. 〔➤ Windows Logo Key Keyboard Shortcuts〕
You can turn this feature off.
To turn it off, just go to the Control Panel, “Ease of Access Center”, then the “Make the mouse easier to use”.
Note that this will also turn off the snap feature using keys. That's too bad, because i would like just the mouse activation off, but the key such as maximize by 【❖ Win+↑】 and minimize by 【❖ Win+↓】, and snap to side by 【❖ Win+→】 and max only vertically by 【❖ Win+⇧ Shift+↑】 … etc are quite useful. Some of these you can do by 【Alt+Space】 then n or x but isn't as convenient.
Extra tip: 2 things i find greatly useful:
Another trick i must have is: Windows: How to swap Mouse Buttons: Right-Click, Middle-Click, while in web browsers.