Please try the following query:
Select Top 1000000 tblComputers.Computer, tblComputers.Username,
tblNetwork.DNSServerSearchOrder As [DNS server], tblNetwork.IPAddress,
tblNetwork.Lastchanged, tblNetwork.DefaultIPGateway, tblNetwork.DHCPserver,
tblNetwork.DHCPenabled, Web40OSName.OSname, Web40OSName.SP,
tblComputers.Description
From tblComputers Inner Join
tblNetwork On tblComputers.Computername = tblNetwork.Computername Inner Join
Web40OSName On Web40OSName.Computername = tblComputers.Computername Inner Join
tblComputersystem On tblComputers.Computername =
tblComputersystem.Computername
Where tblNetwork.DNSServerSearchOrder <> '' And tblNetwork.IPAddress <>
'0.0.0.0' And tblNetwork.IPEnabled = 1 And tblNetwork.IPAddress <> '' And
tblComputersystem.Domainrole > 1
Order By tblNetwork.DNSServerSearchOrder