At last, you can now debug the .NET Framework code, and can have a detailed look at the code, and not just the signatures :)
Previously, Scott Gu announced in his Blog that we will be able to see the Framework code, but no idea how; as it wasn't available to everyone.
Luckily, Shawn Burke finally gave us the exact route to the magic! in this post.
I advice you to read Scott Gu's post about this new feature
Happy Programming, and enjoy Microsoft's magic ;)