How to encrypt databse file

Question

I am using sql server express 2005 for my project along with visual studio
i have created databse file for my project, i wnt to encrypt dthose files using
cryptography technology available in .net framework..i knw it can be done, but dont knw how to do it

if anybody know how to encrypt file, please give me detailes step or link to any such article

thanks in advance