If you think what you see around here is good enough, I'd go for that. The Snitz forums have proven themselves over time as a relatively fast and stable forum (there are currently over 12,000 members, with more than 34,000 posts).
However, if the Snitz forum has too much features, you may be better over cresting a solution yourself. Although you can take the source of this forum as the basis for your own project, and strip what you don't need.
If you want to take this on yourself, I recommend a book like "Beginning Dreamweaver MX 2004". I am a bit biased as I am one of the authors of that book, but I know the book covers the areas you need to know more about to take up a task like this very well. You'll need to know how forms work in ASP, how to connect to a datasource, how to insert and update records in that datasource, how to link detailed pages to lists (master-detail scenario's) etc etc.
It's difficult to say in a post like this: "do this and do that, and it will work". With a book, you'll get a solid understanding of the underlying technologies which is important for a project like this.
Other books you could take a look at are Beginning / Professional ASP 3.0 or Beginning ASP Databases.
In addition to books, you may want to take a look at these sites:
(for their simple and outdated messageboard, look here: http://www.asp101.com/resources/aspforum_revisions.asp
(for the open source Snitz forum)
I'll be more than happy to answer specific questions related to building a message board. However, the question is currently a bit too broad to answer at once.
Investigate any of these resources, see if they make sense. If you need more help, please let me know.
Everyone is unique, except for me.