Ok you got a few options,
Using Xfire--------www.xfire.com it has a feature on there to do it.
Using the halo feature------adding "-screenshots" to your target line in you propeties. saves them in a folder off of your C:drive.
Using the "prt scrn" button top right of keyboard. only takes one so you have to paste and save it in paint.
Using fraps-----www.fraps.com, this is the best feature using F10 to take shots, it stores loads in a folder.