Doing this isn’t nativly suppoted in 2000. <a href=”http://windowsitpro.com/article/articleid/14035/how-do-i-encrypt-fields-in-sql-server.html”>Here</a> is an article about it. I have done it by using System.Security.Cryptography in .net and either binary, varbinary, or image data type in the database. You can also convert the bytes to a base64 encoded string in .net and save it in the database in a varchar field. Regardless doing this in .net requires you to encrypt and unencrypt the data via code each time. (You could write a wrapper around the db object to do this automaticaly.)
You might want to use something a little more current than SQL 2000. That was released 10 years ago and there have been 2 versions released since then with another version being released in the next few months.