To www or not to www, that is in the URL …
I have said that incoming links are very important. That is, you want to have the most incoming links to your pages possible, from the most relevant sites possible. But should you link as www.mywebsite.com or just use mywebsite.com?
Many of us are predisposed to including the www at this point, even though most of the time the www is irrelevant (with www and without www will usually take you to the same place). Still others see the www as extraneous and leave it off and many times you see the www omitted on billboards, vehicles and ads. The answer is either, but not both.
The issue is that most search engines (Google lets you declare a preference in Webmaster Tools) will see these as different and index each separately dividing the rank for the content between the two. This is not desirable.
Still another reason is to generate more incoming links. Case in point, press releases get syndicated in a lot of places and provide good incoming links to your site. Sometime ago I was trying to be aesthetically clean and started leaving the www off the URLs in press releases I was producing. Later when I checked, I found in older releases where the www had been included the URL was linked, but not was linked when the www, was left off !
The bottom line here is using the www, and in some cases even adding the (yuck!) http:// can work to your advantage. The only place leaving it off may help, is in your print ads, billbords, etc.
BTW — I busily edit out all of WordPress’ auto-linking to the fictitious www.mywebsite.com site, otherwise this blog would have many links to it.
If your seeking help with a Windows-based server (IIs), this is a good article on 301 redirects:
http://www.jlh-design.com/2006/08/301-redirects-in-asp-on-iis-server/