Give this a shot:
Select Top 1000000
tblAssets.AssetID,
tblAssets.AssetName,
tsysAssetTypes.AssetTypename,
tsysAssetTypes.AssetTypeIcon10 As icon,
tblAssets.IPAddress,
tblAssets.Lastseen,
tblAssets.Lasttried,
tblDiskdrives.Description,
tblDiskdrives.FileSystem,
tblDiskdrives.Caption,
tblDiskdrives.Volumename
From
tblAssets
Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
Inner Join tblDiskdrives On tblAssets.AssetID = tblDiskdrives.AssetID
Where
tblAssetCustom.State = 1
AND tblDiskdrives.DriveType = 5 -- Compact Disc
AND tblDiskdrives.Size > 0 -- not blank