Does this lens fit a Nikon D3000?

Rokinon FE8M-N 8mm F3.5 Fisheye Lens
http://www.amazon.com/...002LTWDSK/

"The ROKINON 8mm lens is designed for digital SLR cameras with APS-C image sensors."

Yes it will fit (buy the Nikon mount version), but it appears to be manual focus.

It is manual focus on all cameras, it's made that way.

Yes, the F mount model will work on your D3000.