I have previously written about IIRF.   Here I go again:  IIRF has now has been updated to v1.2.15. 

IIRF is Ionic's Isapi Rewrite FilterIt is a small, cheap, easy to use, URL rewriting ISAPI filter that combines a good price (free!) with good features. It is fast and powerful. It works on IIS 5.0, 5.1, 6.0, and 7.0.

You may have heard about the Rewriting Module for IIS7 from Microsoft.  This is not that thing.  This is a rewriter for IIS6 or 7. 

It works with regular expressions. It's fast.  It's written in C. It's open source.  It does not require the .NET Framework.  It works with PHP, Ruby, ColdFusion, JSP, ASP.NET, and anything else you can run on IIS.

Check it out.