A quick report:
SELECT vc.Name, vc.Domain, vc.[User]
FROM vComputer vc
LEFT JOIN Inv_AeX_OS_Add_remove_Programs arp
ON vc.Guid = arp._ResourceGuid
AND arp.Name =
'Your Software Here'
WHERE arp._ResourceGuid IS NULL
AND vc.IsManaged = 1 -- Only machines with Altiris installed
AND vc.[OS Name] LIKE '%Windows%' -- In case you have Unix/Mac/etc