In MS SQL 2005 go to MS SQL books online and look for "encryption [SQL Server], columns"
In MS SQL 2000 i don't know anyt way of doing it. MS SQL 2000 help:
Microsoft® SQL Server™ encrypts or can encrypt:
Login and application role passwords stored in SQL Server.
Any data sent between the client and the server as network packets.
Stored procedure definitions.
User-defined function definitions.
View definitions.
Trigger definitions.
Default definitions.
Rule definitions.