Where can I prevent wordpress from removing www from url

Currently when I go to http://www.anydomain.com on my wordpress install, the www. is stripped and only the http://anydomain.com is displayed on the fly.

I need the site to load either the http://www.sitedomain or http://sitedomain depending on what the user typed. I don't want any domain manipulation to occur.

The reason for this is I have 2 servers, one development, one live. This allows me to easily view either by pointing my 'hosts' file to dev version.

Is this possible in WP ? If so, can someone tell me where to stop this www. strip from occuring. It is not in .htaccess, I have looked.

I am operating a multi-site version.