Does the Nikon D3100 use any Nikon lens for autofocus?
I know on the D3000 some don't auto focus so I was wondering if this one did
such as the AF NIKKOR 50mm f/1.8D or would it have to be AF-S?
I'm pretty sure you would need the 50mm 1.4 to auto focus. It's a bit more in cost. Check Nikon's site and look at the AF portion for the lens you want… You're on teh right track though.
Only AF-S lenses.
To get the features of the D3100 and use AF or AI manual lenses, you would have to buy the D7000 camera.
Entry level cameras assume the person it going to be buying the new, ultra fast auto-focus AF-S lenses.
You can still use AF lenses, because they are compatible with the cameras light meter. In fact 1) there's a neat electronic rangefinder in the viewfinder and remember, for decades photographers had NO auto-focus cameras or lenses.
Only lenses with the AF-S designation will autofocus with the D3100, so something like the AF Nikkor 50mm f/1.8D won't autofocus.
However, you have two other more expensive alternatives. One is the AFS Nikkor 35mm f/1.8G and the other is the AFS Nikkor 50mm f/1.4G. If you had payed attention to the fact that the D3100 lacked an autofocus motor which means you'll have to pay more for lenses that has an AFS motor, then you could've got the D90 which doesn't cost much more than the D3100. The good news is that any lens you do buy today will still be "state of the art" and in high demand 10 years from now, while cameras will soon become obsolete within a year or two.