Will the boat be on a trailer when not in use, or will it be kept in a slip? If on a trailer you won't need any bottom /anti-fouling paint. Clean the old bottom paint off, starting with use of high pressure spray (home or car wash), which will likely get a lot of it off. Then get the rest with either a stripper or wet sanding as mentioned above (or, if what's left is way underneath and can't be seen short of laying under the boat...forget it, leave it there!
). Then paint the entire hull with your "regular" paint. If you are going to keep it in a slip, clean the old "grunge" (the dried on moss/dirt) off the bottom with a high pressure spray and/or hose and brush. Some of the bottom paint may come off also, but that's OK. When it has dried, go and give it a couple coats of botttom paint, put it in the water and enjoy it. Not exactly by-the-book maybe, but you have to recoat the bottom every season anyway. Of course if you're going to race the boat, this "good enough" attitude won't do!
steve parsons (saabdrver-at-aol.com)