i've heard that some folks say to put a cut potato in the tank and all the snails will attach themselve to it. i tried it, snails are smarter than they look, they jump off when you move the potato.. lol.
best cure i know for snails is red jewel cichilds.. when i used to keep the fry i kept them in a snail infested 10 gallon tank. it was great, when there was lots of food because we were feeding the fry often the snails would multiply, and then the fry would get big enough to eat the snails and the tank would suddenly be clean.