Couple of links (Which I need to have a further read of)

Legacy Url Routing - converting your ASP.net application to a MVC, how to route the old aspx page to redirect to the MVC required view.

Asp.Net Routing Debugger - allows you to type in URLs and it shows which routes match it (nice :) )

three Common ASP.NET MVC URL Routing Issues - as title suggests

(in a nut shell)

1. Register the mappings in the correct order
2. Set the redirect of the default.aspx
3. parameter names match