Annotate code in VS 2010 without changing that code

I have just started a new job, and am trying to familiarise myself with a large C# solution, of 330 odd projects. Ideally I would like to attach comments and questions to pieces of code without actually editing the code itself.

Is there a tool I can use to annotate C# source code without actually editing the code itself. Ideally I would like a 'bubble' type comment mechanism, similar to how MS Word shows comments in a a document.