username & pass word: C#

hi

i want cretae an algorthm for..encryption and decryption of "Pass Word","Use Name"........

Presently i dont have any idea about dis....i googld sum codes using

using System;
using System.IO;
using System.Security;
using System.Security.Cryptography;
using System.Runtime.InteropServices;
using System.Text;


hmm...coool...and  simple....but can u help me to build ....a simple alogorith with two functions.....

one for encrypt and other for decrypt....


and methods for "diffrent algorthms..."...pls hep me...