The .com TLD works for both the www and non-www version of the site. But to be sure that you do not have an indexing problem, use a 301 server side redirect to force the non-www version to the www version.
http://www.bing.com/community/forums/t/657920.aspx
An SEO Monopoly can dramatically increase the odds of a searcher finding out about your product or service.
