Running Version: 6.0.0.22
I am looking for the code to ignore multiple drive letters (like CDRom Drive, USB Drives, etc.)  I really only want to see low disk space on Drive C:\
Here is my current code:
Select Top 1000000 tblAssets.AssetID,
  tblAssets.AssetUnique,
  tsysOS.OSname,
  tblAssets.Description,
  tblDiskdrives.Caption,
  Cast(Cast(tblDiskdrives.Freespace As bigint) / 1024 / 1024 As numeric) As
  free,
  Cast(Cast(tblDiskdrives.Size As bigint) / 1024 / 1024 As numeric) As
  [total size],
  tblDiskdrives.Lastchanged As [last changed],
  tsysOS.Image As icon
From tblAssets
  Inner Join tblDiskdrives On tblAssets.AssetID = tblDiskdrives.AssetID
  Inner Join tblOperatingsystem
    On tblAssets.AssetID = tblOperatingsystem.AssetID
  Inner Join tblComputersystem On tblAssets.AssetID = tblComputersystem.AssetID
  Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
  Inner Join tsysOS On tblAssets.OScode = tsysOS.OScode
Where Cast(Cast(tblDiskdrives.Freespace As bigint) / 1024 / 1024 As numeric) <
  5120 And Cast(Cast(tblDiskdrives.Size As bigint) / 1024 / 1024 As numeric) <>
  0 And tblComputersystem.Domainrole < 2 And tblDiskdrives.DriveType = 3 And
  tblAssetCustom.State = 1