This should get you what you need.  A caveat is that if a machine is part of multiple Organizational Groups, then it will list all of them.  We can always filter out specific ones if you want.

SELECT ci.Name
              ,i.Name AS [Organizational Group]
              ,CASE WHEN ctr.IsActive = 1 THEN 'Yes'
                          WHEN ctr.IsActive = 0 THEN 'No' END AS PoweredOn
              ,CASE WHEN lastTime.Event = 'Logoff' THEN 'No'
                          WHEN lastTime.Event = 'Logon' THEN 'Yes'
                          ELSE 'N/A' END AS UserLoggedOn

FROM vRM_Computer_Item ci
JOIN Inv_Client_Task_Resources ctr
   ON ctr._ResourceGuid = ci.Guid
JOIN ScopeMembership sm
   ON sm.ResourceGuid = ci.Guid
JOIN Item i
   ON i.Guid = sm.ScopeCollectionGuid
LEFT JOIN (SELECT _ResourceGuid, _eventTime, clo.[Event]
                    FROM Evt_AeX_Client_LogOn clo
                    JOIN (SELECT MAX (_id) AS ID
                               FROM Evt_AeX_Client_LogOn
                               GROUP BY _ResourceGuid) maxid
                       ON maxid.ID = clo._id) lastTime
   ON lastTime._ResourceGuid = ctr._ResourceGuid

The logon/logoff information is updated when the Altiris Agent detects one of those events on the PC.  So, it is almost "realtime".  The biggest bottleneck will be the NS itself processing the NSE's and then updating the SQL tables.

As for the IsActive, this is a "heartbeat", if you will, from the Client Task Agent (Task Server).  I believe they "check in" every 10 minutes or so, by default.  So, fairly accurate and up-to-date.