Mod-rewrite - Help me!!

This one's confusing me, and I hope someone can clarify this for me.

I'm trying to have all non-www pages in a subdirectory redirect to a www option.
Everytime a non-www page is accessed in the browser, I want it to have a 301-redirect to the www. version:

http://domain.com/subdirectory/pagenames.html   REDIRECT TO
http://[B][U]www[/U][/B].domain.com/subdirectory/pagenames.html

Code (markup):

What's the htaccess code to incorporate?

Thanks for the help guys!

 

This should help you:

# mod_rewrite in use
Options +FollowSymlinks
RewriteEngine On
RewriteCond %{http_host} ^domain.com [NC]
RewriteRule ^(.*)$ http://www.domain.com/$1 [R=301,L] 

Code (markup):

 

Thanks! I'll give this a try and keep you posted...