This is a question that seems to be coming up more and more. Unfortunately I do not know of any
VB.NET boards that are open source (PHP has one ala
www.phpbb.com) that you could use as a reference however, when you think about it, a forum is actually ruidementary calls to a database and an interface to display those posts.
At the most basic level you need a Users table that will contain your user information and you will authenticate people against that.
You will have a table of top level categories (in P2P regards they have C#,
VB, ASP.NET, XML, etc)
A table that will have categories related to the top level categories (In the case of the ASP.NET forum we have 1.1 Beginner and Professional 2.0 Beginner and Professional etc)
Another table that contains the threads of the given forum (this is related to the forum)
And, lastly, a table that contains the the posts to threads, etc which is related to the above threads table.
The methods for retrivieng this data is truly ruidmentary.
hth
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I will only tell you how to do it, not do it for you.
Unless, of course, you want to hire me to do work for you.
^^Thats my signature