http://www.nikonchat.com/digital-nikkor-lenses/

Question about Nikon cameras?
I have a Nikon N75 film SLR camera that keep.Can whick I can buy a Nikon D40 SLR camera digital and use the lens with my N75 and the D40? Yes they are Nikon and Nikkor AF. If requested by the N75 is a body that accepts FG or D AF lenses.
As Ben said, the Nikon D40 is a unique animal in the catalog Nikon D-SLR in that it can only autofocus with the new "AF-S" lenses. You will able to manually focus Nikkor on a D40. You would be wiser to look at the Nikon D80 or D200 that can autofocus with AF. You can also find more D50 or D70 available – and can also autofocus with AF can. They seem to have some manual focus lenses as well. compatibility with earlier versions of Nikon "F" Mounting is general. For manual focus lenses, research them specifically for compatibility – some do not turn correctly meters the new Nikon cameras:. – Disclosure I am the owner of www.lenslenders.com in Canada.
Olympus EP-1 autofocus demonstration and size comparison