First determine what kind of a snail it is, based on this article:
http://plantgeek.net/article_viewer.php?id=14. If it's not a ramshorn snail, you shouldn't be worried. I was afraid of snails too, but after they hitched a ride to my tank (on plants, of course), they turned out to be EXCELLENT algae eaters! (That is, the pond snails.) I now keep them in all of my tanks. I now LOVE snails
If you don't overfeed your fish, and keep your tank (especially gravel) very clean, you shouldn't have any problems with the snail population. I don't overfeed my fish, and my snail population seems to stay very small.