Try this
Select Top 1000000 tblADusers.Username,
tblADusers.Displayname,
tblAssets.AssetID,
tblAssets.AssetUnique,
tblSoftwareUni.softwareName,
tblSoftware.softwareVersion
From tblAssets
Inner Join tblSoftware On tblAssets.AssetID = tblSoftware.AssetID
Inner Join tblSoftwareUni On tblSoftwareUni.SoftID = tblSoftware.softID
Left Join tblADusers On tblAssets.Username = tblADusers.Username And
tblAssets.Userdomain = tblADusers.Userdomain
Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
Where tblSoftwareUni.softwareName Like '%Office 2003%' And
tblAssetCustom.State = 1
Order By tblAssets.AssetUnique