domain mapping with 'www' and not resolving

Hi

Domain mapping at site level is defaulting to no www so it's just http://domain.com however my multi site is using www and I need consistency - so I need http://www.domain.com.

Other than that I can't get it working even though the *. DNS of the domain is pointing to my server IP{.

Can you please advise.

Thanks

Glennyboy