A:
The D3100 has a standard Nikon F mount with AF contacts. The F mount is the same mount Nikon has used for ages. All Nikon /.Nikkor lens fit this mount. There are a few older lens that may not fit due to manual connections, but those are highly specialized and few and far between. Keep in mind that a non-digital 35mm lens is going to have a focal length that is different on a digital camera.
For any given focal length on a Nikon DSLR, you'll have the same angle of view (apparent magnification) that you would use a 50% longer lens on a 35mm camera. That is due to angle of view from the lens to the media. Film cameras have a different angle of view compared to digital cameras.
In order to see what focal length you'd need on a 35mm camera for the same angle of view, multiply the focal length by 1.5x (it's actually slightly more, but it's rounded).
So, a 28-300mm analog lens on a Nikon DSLR would give you approximately the same angle of view you'd have using a digital 42-450mm lens on a 35mm cameras.
I cribbed this from this much more detailed description of the phenomenon:
http://forums.steves-digicams.com/nikon-lenses/126063-35mm-digital-lens-conversion.html