Google and most search engines see domain.com and www.domain.com as two different sites/pages. The problem is if you get links to your site, some with the www and some without, your total number of links isn't the true total. It's split between the two. Using .htaccess and mod_rewrite, you can do a 301 redirect to the www version.
Below is some code that will help:
rewriteEngine on
RewriteCond % ^domain.com$
RewriteRule ^(.*)$ http://www.domain.com/$1 [R=301,L]
The first line turns the rewrite thing on, if it was off.
The second line checks for the host. The ^ means the beginning and the $ means the end.
The third line, no checking what comes after the host, will forward any directories/files from domain.com to your domain with the www. The $1 is the variable that hold the directories/files, so yourdomain.com/some/directory/file.html would have $1 equal to some/directory/file.html. The R=301 forces a 301 permanent move redirect. Google will then see it as one domain. The L says it's the last rule. If you add other rules and leave off the L, it would go through them all before finally redirecting.
Please let us know if you have any further questions by submitting a support ticket.
