[drupal-support] How to handle the www subdomain?

[Steve Dondley]

I have an apache server running Drupal 4.6 and php 4.10.  I notice that 
when my domain is accessed via www.mydomain.com, it has a different user 
session than my domain at mydomain.com (with no www subdomain).   In 
other words, I can  be logged in at mydomain.com yet logged out at 
www.mydomain.com and vice versa.

I notice this isn't the case at drupal.org, however.  When I log out at 
www.drupal.org, I also get logged out from drupal.org.  Does anyone know 
how to accomplish this?  Do I need two settings.php files and change a 
php setting or two?  Or is this an apache configuration issue?