Share Tables Method

Architecture of subdomains for different sections/departments sharing maximum number of tables
http://drupal.org/node/54649

consen - http://drupal.org/user/13462
http://consen.org/

We have the Editorial sections sharing the tables
$db_prefix = array(
'default' => 'EXTRA_',
'users' => '',
'sessions' => '',
'role' => '',
'authmap' => '',
'sequences' => '',
);
and the Drupal files in the subdomain extra.mainsite.org

This same we have done for the administration section
admin.mainsite.org
and for the Office section
office.mainsite.org

Note: this is a description for entirely different databases, and not directly relevant to what we need to do:
Multisite with drupal for dummies
http://drupal.org/node/107347

A completely different method: custom node types and templates based on node type!
http://drupal.org/node/114719

Customising the full page layout and sections based on path
http://drupal.org/node/46027

Groups-related discussion -- pretty general
http://groups.drupal.org/node/1792
Good place to go back and tell Moshe he's wrong:
if the subdomain is really important, then you probably do need to run two drupal sites with different databases. the code can be symlinked between the two if you don't want to truly diuplicate the files but thats a minor point.
-- that Webchick is a genius.

Drupal multi-site setup documentation: request for comments
http://drupal.org/node/104340
- useful and I should report back here, check for the "I added this at /node/XX" comments