Canon have changed their mount just once, the old one being the FD mount the current one the Ef mount to fit all EOS cameras. They also do the Ef S mount which fits the 300D, 350D,20D,30D and 400D.
You can get an adapter to mount FD on EF cameras made by SRB at
www.srbfilm.co.uk which has to contain an element which multiplies focal length by 1.6. As you say all functions have to be manual as the camera can't ''talk'' to the lens. Think cost is about £45. Hope this helps.