Read it
https://www-secure.symantec.com/connect/forums/altiris-report-find-out-computers-software-not-installed
Query
SELECT vc.Name, vc.Domain, vc.[User]
FROM vComputer vc
LEFT JOIN Inv_AeX_OS_Add_remove_Programs arp
ON vc.Guid = arp.guid
AND arp.Name = 'Your Software Here'
WHERE arp.guid IS NULL
AND vc.IsManaged = 1 -- Only machines with Altiris installed
AND vc.[OS Name] LIKE '%Windows%' -- In case you have Unix/Mac/etc