This tutorial describes tweeting with media (pictures) in .NET via the Twitter REST API, using the LinqToTwitter library.
This tutorial / walkthrough describes installing LinqToTwitter into a Visual Studio .NET project and using it to make plain-text tweets.
Code and algorithm to hashtag a string in ASP.NET Web Forms. Written in VB.NET, includes working demo.
Expanding on my earlier post about auto-hashtagging text: Now, we can put the hashtagged text into a MySQL table.