[via Scott Guthrie]
ASP.NET 2.0 offers up a new feature called “URL Mapper” where you can map specific friendly URLs to parameter based URLs. For example, you can map http://www.foo.com/products/cookbooks.aspx to http://www.foo.com/products/catalog.aspx?id=1. The downside is that the paremeter URLs are hard coded. In other words, you can’t make these dynamic. Scott Guthrie explained in a post why the ASP.NET team didn’t make the URL Mapper more feature rich, such as supporting RegEx patterns. The primary reason is because of bandwidth (time).
However, Christopher Pietschmann posted a solution adding RegEx support for URL rewriting in ASP.NET 2.0.