Constructing a simple interpreter

I would write it in ANTLR. Write the grammar, let ANTLR generate a C# parser. You can ANTLR ask for a parse tree, and possibly the interpreter can already operate on the parse tree. Perhaps you'll have to convert the parse tree to some more abstract internal representation (although ANTLR already allows to leave out irrelevant punctuation when generating the tree).

It might sound odd, but Game Scripting Mastery is a great resource for learning about parsing, compiling and interpreting code.

You should really check it out:

http://www.amazon.com/Scripting-Mastery-Premier-Press-Development/dp/1931841578