C# code review and compare

Question

I want to decompile a C# 2010 application. The only thing I have to work with is the deployment and setup project that I obtained from a contract shop. (I am pretty certain the code I obtained from the contract shop is not the most current version of the code.)


In addition, I would like to know what a good open source (free) tool and/or visual studio.net 2010 professional featuret I can use to compare the C#.2010 code. Basically I want to compare code that is in a visual studio.net professional environment to the same some that is obtained from a decompiler tool.

  Basically I would like to know if the professional version of visual studio.net 2010 has these features? if so, what are they and how do I access these features.

  If this is not avaialble, then what open source (free) tool(s) would  you use? Of the tools you recommend, would you let me know if they are setup to work well with each other? Possibly there is one open source tool that would accomplish this goal?