I offer two products which have the ability to redirect the 'www' to 'non-www' or the other way around, to put the 'www' in if it wasn't supplied. These don't need IIS configuration changes and are therefore suitable for shared hosting.
These are:
iFinity Friendly Url Provider
iFinity Url Master
Both modules are drop-in replacements for the standard DNN friendly Url provider/ Url Rewriter. Both modules offer 'friendly urls' and offer 301 redirects for:
- unfriendly urls (/home/tabid/36/default.aspx)
- wrong subdomain (www not included, or www included and not wanted)
- default.aspx or site root -> home page
- mixed case -> lower case
The Friendly Url Provider is free with source available
The Url Master module is an advanced version which has a GUI interface, Customised Urls and 301/302 redirects and many more features
One of these modules may provide the solution you are after.