On October last year Scott Guthrie blogged about Microsoft plans to release the .NET Framework Source Code to enable debugging support with Visual Studio 2008, well the moment is come and now you can browse and debug the source code of the following libraries:
.NET Base Class Libraries:
System, System.CodeDom, System.Collections
System.ComponentModel, System.Diagnostics
System.Drawing, System.Globalization, System.IO
System.Net, System.Reflection, System.Runtime
System.Security, System.Text, System.Threading, etc.ASP.NET (System.Web, System.Web.Extensions)
Windows Forms (System.Windows.Forms)
Windows Presentation Foundation (System.Windows)
ADO.NET and XML (System.Data and System.Xml)
And soon the LINQ, WCF and the Workflow Foundation will be added.
You can find a detailed post by Shawn Burke that explains the exact steps on how to enable this.
