Just took the leep and it arrived this morning!! All look well so far, I picked this lens as it has AF Auto Focus and V R Vibration Reduction. I will post again after the weekend is over after i have had a good play around and let you know for sure!!
When searching for compatible lenses look for "DX" D3100 is a DX format camera. And "AF-S" The means the lens has the autofocus motor built in, which the D3100 needs. Just "AF" would mean you have to manual focus on the D3100.