to www or to not www - how to make it www???

Sorry if the title is confusing.

If someone goes to http://www.mydomain.com/forum they are spat back to http://mydomain.com/forum

If you go to http://www.mydomain.com/forum/ it is all fine, and the domain does not refresh.

How to I fix this so everything has the www in it?

 

Can you please post the .htaccess file located in mydomain.com's public_html.

Jay

 

php_value register_globals On
php_value session.gc_maxlifetime 72000
php_value session.cookie_lifetime 72000