Recently I migrated an ASP.net site to ASP.net MVC site. Earlier there were two host headers one mydomain.com and another is www.mydomain.com. My SEO says you should use only on
Unfortunately, the URL rewrite module does not work with IIS6 (only IIS7 or greater). Have you considered creating your own HttpModule, something like this this?
IIS 6 how to redirect from http://example.com/* to http://www.example.com/*
Or you could potentially use a 3rd party solution like one of these:
http://iirf.codeplex.com/
http://www.urlrewriting.net/149/en/home.html
http://www.isapirewrite.com/
http://urlrewriter.net/