I came across a blog post.  The post provided a link to a tool you could use to download the available .net source code.  Microsoft allows you debug into the framework.  If you are like me you may just want to be able to browse the source code at your leisure.  Here is a tool that will download the the pdb and corresponding source code files. 

http://www.codeplex.com/NetMassDownloader

Here is the command line I used to download the source files:

PS C:\SRC\NetMassDownloader\Debug> .\NetMassDownloader.exe -d 'C:\Program Files\Reference Assemblies' -o C:\src\symbols\
MassDownload

Happy Coding

Bill