IIS 6 - Setting up 301 redirect for non-www to www for SEO
Solution 1:
You should define two websites in IIS; one should be a "dummy" site that only answers to "company.com" and redirects to "www.company.com", and the other should be your "real" site that answers to "www.company.com".
you can't do both on the same site using IIS redirection, or you'll be stuck in an infinite loop (as you already noticed).