This article describes how to 301 redirect the non www to www. Example http;//mywebsite.com.au to http://www.mywebsite.com.au

Login to your control panel.

1.. If it is there remive the non www domain from under Web > Websites > Click on domain link > Remove the non www site pointer by clicking on the red x
2.. Create a new website and select mywebsite.com.au (replace this with your domain) then click create website.
3.. Go to Web > Websites > Click on the new entry you added above.
4.. In the home folder tab select the "Rediction to URL" button and enter http://www.mywebsite.com.au (replace mywebsite.com.au with your domain)
Ensure you select "A permanent redirection to this resource" as this makes it 301

Click on Update.

Now all requests for the non www with 301 Redirect to your www domain.