Found a field which contains this data so it is easier:
Select Top 1000000 tblAssets.AssetID,
tblAssets.AssetName,
tblAssets.Username,
tblAssets.IPAddress,
tblAssetCustom.Manufacturer,
tblOperatingsystem.Caption As Windows,
TsysChassisTypes.ChassisName
From tblAssets
Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
Inner Join tblSystemEnclosure
On tblAssets.AssetID = tblSystemEnclosure.AssetID
Inner Join tblOperatingsystem
On tblAssets.AssetID = tblOperatingsystem.AssetID,
TsysChassisTypes
Where tblAssetCustom.State = 1