This is my Messenger created with VB 2010, using MySQL Connection.
1) To test this program you need to create a database in your server, named: "messenger", then a table: "users". In users add two fields: "username" and "password". Create them, and add some data there.
2) Try to login with your data

You will see that u can access the program with any account, so, basically it just for testing :P

Images:

1. Login form
2. Show that form if the username is not correct or doesnt exists in database
3. login OK
4. Chat window

Screenshots