YetAnotherForum.net

Not terribly well documented, current "release" version is 0.9.6, but it looks very cool compared to previous free offerings (Snitz, et al) I have come across

ASP.NET (C#) front-end
SQL Server back-end (so I guess MSDE would work too)

Pretty trivial to install, has the ability to have the interface language changed via an XML file (only English, German and Norwegian in the release so far but I'm going to work on Swedish).