Please try the following:
Select Top 1000000 tblAssets.AssetID,
tblAssets.AssetName,
tblAssets.Domain,
tblAssets.IPAddress,
tsysIPLocations.IPLocation,
tblAssets.Firstseen,
tblAssets.Lastseen
From tblAssets
Left Join tsysIPLocations On tblAssets.IPNumeric >= tsysIPLocations.StartIP
And tblAssets.IPNumeric <= tsysIPLocations.EndIP
Order By tsysIPLocations.IPLocation,
tblAssets.IPNumeric