You can now develop windows based or web based Facebook Applications using your favorite .NET language, be it C# or VB.NET. All you need is a Facebook account, Visual Studio Express and the Facebook Developer Toolkit for .NET. Information about the Facebook Developer Toolkit can be found here. The tooIkit makes it incredibly easy to develop Facebook Applications based on the Facebook Platform. The toolkit also includes WPF and LINQ examples. I would strongly recommend you to check out the following links before going ahead and downloading the toolkit:

1) Video: Facebook Developer Toolkit Walkthrough (Windows Forms)
2) Video: Facebook Developer Toolkit Walkthrough (ASP.NET)
3) Facebook Quickstarts

Detailed information on the Facebook Platform can be found here.

Cheers,
Raj

~~~ CODING FOR ETERNITY !!! ~~~