Windows 7 allows you to activate a window on mouse hover action.Using below mentioned steps you can enable this feature:
1. Open the Control Pane from Start Menu. Click on Ease of Access category.
2. From Ease of Access Center Click "Change how your mouse works".
This will launch the "Make the mouse easier to use" panel as shown below.
Alternatively you can open this windows by typing mouse in the "Search Files And Programs" box of the start menu. Then select "Change how your mouse works" from the search result.
On above panel select the checkbox for the option "Activate a window by hovering over it with the mouser ". Now Click Apply and OK.
Now when you move mouse over any window it will become active.