Display sub-categories based selected Parent Category

Hi gurus,
I was wondering if anybody know hows to modify the existing category widget to only display the categories within the selected parent category.
Example:
If my categories are structured like:
– Computers
-Laptops
-Desktops
-Software
– Electronics
– Cameras
– Audio/Video

If a somebody is viewing posts in the Computers category I would like the categories widget in the side bar to only display Laptops, Desktops & Software..

Is there a way to get this done? Is anybody familiar of a plugin that maybe do that?
Thanks!