<p>As a lot of people pointed out in <a href="https://stackoverflow.com/questions/4724/learning-lisp-why">this question</a>, Lisp is mostly used as a learning experience.  Nevertheless, it would be great if I could somehow use my Lisp algorithms and combine them with my C# programs.
In college my profs never could tell me how to use my Lisp routines in a program (no, not writing a GUI in Lisp, thank you).
So how can I?</p>

Try these .Net implementations of Lisp:
IronScheme
IronScheme will aim to be a R6RS
  conforming Scheme implementation based
  on the Microsoft DLR.
L Sharp .NET
L Sharp .NET is a powerful Lisp-like
  scripting language for .NET. It uses a
  Lisp dialect similar to Arc but
  tightly integrates with the .NET
  Framework which provides a rich set of
  libraries.