I had the stowaway problem when I was first starting out - the snails appeared on mass one day during my fishless cycle - I panicjed and started looking around for the best "cure" - although, as soon as I put fish in, they vanished - now I haven't seen one in months!
I'd say leave it be and just see what happens if there arent too many.
Think of them as free fish food - Live food is good for your fish.
Also, some people say that only loaches eat snails - this is true to some extent but if you see them on the glass or lid, pick them off and squeeze them between your fingers - As well as being very satisfying, you can drop the squished beasties in the tank and anything will eat it!
As I said - mine dissappeared on it's own.
I then missed them and went and bought 2 snails.
I have 1 zebra snail and an Apple Snail.
The apples are quite cool looking with their coiled shell and their little trapdoor flap thing!
(those of you that have apples can probably relate!)
