On our Windows/ColdFusion servers at www.gowesthosting.com we run Helicon APE (and on our older servers, ISAPI Rewrite, also by Helicon) which lets you use standard Apache .htaccess files to create rewrite rules for any website. 

Here are a few quick useful snippets for rewriting any URL to include the 'www' prefix. This is good practice, preventing the 'duplicate content' penalty from Google which can occur when a site is available under two addresses, as well as forcing consistency to visitor sessions. This is especially critical in eCommerce sites where a user's session may not be persisted when jumping from a 'www' to 'non-www' page. 

 

RewriteEngine on
rewritecond %{http_host} ^domain.com [NC]
rewriterule ^(.*)$ http://www.domain.com/$1 [R=301,nc]

just replace "domain.com" with your actual domain, and you should see http://yoursite.com/ gets redirected to add the 'www' prefix automatically.

TIP: be sure to use the 'www' anywhere you link to your site, or when connecting any third-party services like PayPal, since a form 'post' from any external source will not be persisted if the page gets redirected.