Please try with this sql:
SELECT TOP 1000000 dbo.tblComputers.ComputerUnique, dbo.tblUsersInGroup.Computername, dbo.tblComputers.Domain,
dbo.tblOperatingsystem.Description, dbo.tblUsersInGroup.Domainname, dbo.tblUsersInGroup.Username, dbo.tblUsersInGroup.Lastchanged,
dbo.Web40OSName.Compimage AS icon
FROM dbo.tblUsersInGroup INNER JOIN
dbo.tblComputers ON dbo.tblUsersInGroup.Computername = dbo.tblComputers.Computername INNER JOIN
dbo.tblOperatingsystem ON dbo.tblComputers.Computername = dbo.tblOperatingsystem.Computername INNER JOIN
dbo.web40ActiveComputers ON dbo.tblComputers.Computername = dbo.web40ActiveComputers.Computername INNER JOIN
dbo.Web40OSName ON dbo.Web40OSName.Computername = dbo.tblComputers.Computername LEFT OUTER JOIN
(SELECT DISTINCT *
FROM (SELECT dbo.tblComputers.Computer AS Domain, dbo.tblUsers.Name AS Username
FROM dbo.tblComputers INNER JOIN
dbo.tblUsers ON dbo.tblComputers.Computername = dbo.tblUsers.Computername
WHERE dbo.tblUsers.BuildInAdmin = 1
UNION
SELECT tsysadmins.Domain, tsysadmins.AdminName AS username
FROM tsysadmins) DERIVEDTBL) localadmins ON dbo.tblUsersInGroup.Domainname LIKE localadmins.Domain AND
dbo.tblUsersInGroup.Username = localadmins.Username
WHERE (localadmins.Domain IS NULL) AND (localadmins.Username IS NULL) AND (dbo.tblUsersInGroup.Admingroup = 1)
ORDER BY dbo.tblComputers.Computer