Sigma 70mm F2.8 EX DG macro

I have Nikon D5100, which has no in built motor. My question is whether Sigma 70mm F2.8 EX DG Macro lens is compatible with my camera or not? Otherwise, will it auto focus with my cam?

I've had a look at the Sigma website and it's still pretty unclear. I would go and try one out at a dealer if at all possible, unless someone else can offer the answer.

I suspect from what I've read that it may be a problem, but I could well be wrong.

John