This is a great program I ran into a while back. It lets you disassemble any program that uses the .net framework.
Explore and analyze compiled .NET assemblies, viewing them in C#, Visual Basic and IL. Now supports .NET 4
Step into decompiled assemblies and use all the debugging techniques you would use on your own code. Get a better understanding of unfamiliar or poorly documented code, by stepping into it straight from the VS debugger.
To Download Click Here