Would these lens work with the Nikon D3100?

Http://www.amazon.com/Tamron-70-300mm-4-0-5-6-Macro-Digital/dp/B0012UUP02/ Would these zoom lens work with the D3100 in both automatic and manual?

It should work, but the sharpness of these $200 70-300mm models is not good. Save your money for a better one.

Look on the amazon site. There's 265 photos taken with this lens from people who bought it.
You get what you pay for. If I were you, I'd buy a refurbished Nikon 55-200mm VR lens.
Once you go over 200mm, it's harder to handhold a lens.

Yes, it will autofocus with your camera. You can also use it in manual focus mode.