Hi HomerJ,
Within the site admin the user listing that you see for the projects is the user base for that project only (and is a smaller subset of the entire user base sen under the Site Users tab).

In order to generate this query, your user accessing Site Admin will need to the correct permissions to query the DB, but you would rung this within a project table (it doesn't matter which one) within any project:

SELECT * FROM .td.USERS WHERE US_IS_ACTIVE = 'Y'

The above query would return a list of the active accounts within your ALM/QC system (replace the Y with an N to return a list of the inactive user accounts within the ALM/QC instance). Just makes sure and replace the qcsiteadmin_db within the <> with your correct qcsiteadmin_db name and omit the <>.

You can also run the same query on the DB itself, or have your DB admin run the query to generate the list.

Hope this helps.
Dan