Nikon Manual SLR coupled with AF-S?

It is possible to mount AF-S lenses on AI cameras such as the FMs, etc. But everyone says they do not work.. well.. before I ruin a roll of film, in what way do they not work, does the aperture stay open fully? Or does it stop down to the highest f-stop the lens has?

I really would hate to be stuck with two primes that are manual, when I have all these AF-S lenses laying around