SQL active user count

I am trying to figure out how to get the list of active users in SQL 2005 with just basic data read/write permissions.

Is there a singular right that I can grant that could allow this to work without giving away the farm?

If run with admin rights/sa the sp_who returns as expected, but with limited rights it returns 0 records.

This is one of the hiccups we have hit while trying to secure our application/database better.

The point is to get the count of the unique user/machine pairs accessing a particular database for licensing counting purposes.