help - www breaks my site

[eluser]bgreene[/eluser]
my site works fine as long as people enter http://ecoland.com but if they enter http://www.ecoland.com the ajax wont work (i presume because that it is looking to http://ecoland.com which it sees as a different address). it gets this value from site_url(blah) i've done a print_r of $_server vars but none of them show me if it is http://www.ec or http://ec. is there some way of routing all http://www.eco to http://eco
many thanks.
Bill