Please don't cross post.
I think that the book you probably would want to look at is:
ASP.NET 2.0 Website Programming: Problem design Solution. It's going to teach you a lot about the site architecture you'd need for something like this and the sample application (the beerhouse) does include some similar community features.
Alternately, you could also look at:
ASP.NET 2.0 Instant Results
It's less about "teaching" developing the sites but it includes several working example applications such as chat and blogs that might be good building blocks for what you want to try to do.
Good luck.
Jim Minatel
Senior Acquisitions Editor
Wiley Technology Publishing
WROX Press
Blog:
http://wroxblog.typepad.com/
Jim's Book of the week:
No book this week - Donate to the Red Cross!
ASP Book
