Need Guidance To Make a Messenger Like Chat Application

hi guys,
firstly as it is my first post, i want to say that i was watching the forum for 2-3 months.
i have a community web site and i want to develop a msn like chat application.

The users will register on my website to use the app.
My database on my webserver (mysql) will have 2 tables.
Table 1 Users: id , status(online or offline), ip .. and other personal data
Table 2 Friend will contain id of the user and id of his friends.

So the mysql database will act as a server which;
- the application produce the user list by looking the friends table(and state if they are online or not by checking their status)
- the application will get the ip's to send text messages.

Also, the application will refresh the user list by sending ping request to ip's of users in the list,if it can not then app will remove the user from the list.

My question is,
I know how to use myodbc, but some lack in network programming. I have been searching the VBFORUMS for 2 days,but what i found is server/client applications using UDP,which did not help me,and also most of them are in VB6(I am using .Net 2003)

Can anyone tell me some walktrough? :(
Regards...