I heard from a friend that soaking new plants in a lemon juice / water mix will kill the snails. Im just not sure how long you do it for and if the acidity can hurt the plants.
You know... call me crazy I dont really mind the little snails. I tried live plants a year ago and just couldn't keep them alive.. even with a special light, and stuff you put in the substrate for them to live on.. but anyway I still have snails in my tank from that failed attempt. I dont see many of them though because my fantails eat them. If you look around places like Petsmart who are infested with the little black snails, they use fantails and common goldies to clear them out of other tanks. Obviously they cant get all of them but the goldies do a good job of keeping them off the glass, plants, and other media in the tanks. In my opinion the snails just add more variety to the fishes diet.
But hey what the heck do I know? I just like fish.