What do I need to make Nikon lens autofocus?

I have a Nikon D3100 and I have three lenses for it. I have the 18-55 kit lens, a 55-200 telephoto and a 50mm 1.4 AF-D. I received the 50mm as a gift and I know that it has to have AF-S in order to be able to use it in autofocus on my camera. I'm wondering if there's a converter/adapter type thing that I can purchase and attach to my lens and camera that will allow me to use the autofocus feature!

Sorry, there's no way to make it autofocus on your camera.

Find a way to exchange it for a 50mm/1.8G or 1.4G.

No there's nothing out there like you have described. You can always manual FOCUS, still very usable and great lens.

With the D3100 if you want a lens to auto focus on it you must buy the Nikon AF-S lenses. There's no adapter that will replace a focusing motor - it must either be built into the camera body or built into the lens. Return the AF 50mm f1.8D and pay the $100.00 or so difference for the AF-S 50mm f1.8G - or learn to manually focus the 50mm f1.8D.

There may well be an adaptor available for your other lenses, but it will only allow you to use the in a manual focusing mode. Mix and match id fraut with problems like this. It's always better to use lenses designed by the camera manufacturer as they have their own electronic language from body to lens.