Using Torn paper brushes

Select the brush from the toolbox
Set the correct size! (beyond 100px)
Set gradient either as FG to BG or FG to Transparent.
Click multiple times to "tear" the edge off.

Importing Photoshop Brushes into Gimp

Download brushes (maybe unzip)
Move file into <gimpDirectory>\Share\gimp\2.0\brushes 

Found on: http://graphicssoft.about.com/od/gimptutorials/ss/install-photoshop-brushes.htm