I've been meaning to write to ask if someone could better explain for me the use of the Drupal module. I know basically what it does but how would one link with other specific sites? Suppose I wanted to have 3 drupal installs of mine, in different locations all allow the users to login with one login for all 3 sites? How do I setup the Drupal core module to do this? Or to work with other drupal sites?
You are very likely better off setting up a "multi-site" with appropriately shared tables. Drupal ID (Drupal module) will require a login of the form: username@site-A.com when logging into site B and vice versa.
hth -K