AFAIK EF and EF-s are different mounts, a camera that uses EF lenses (full frame like the 5DMkII and 1Ds) cannot take the EF-s lenses which are designed for smaller sensor cameras like the 50D etc. The smaller sensor cameras however, can take both.
Image stabilisation works by reducing the shaking from hand-holding the camera or using it on a monopod. It allows you to take photos at a slower shutter speed. As far as photographing fish and sport subjects, the subject will be moving too fast to use slow shutter speeds anyway, so image stabilisation is of little benefit. By the time you have a shutter speed fast enough to stop the action to get a sharp pic, the vibration from handholding is almost entirely eliminated as well. It's therefore of most use in situations where your hands shaking are the only problem where the subject is moving very slowly or fixed in one spot. Phew! Hope that all makes sense!
Manual focus lenses are very rare these days, chances are you'd have to order one or buy secondhand. I'd say 95% of new lenses sold for digital SLR's will be fully autofocus but be sure to ask if buying an old secondhand lens.
HTH!
