function IntToDriveType(Value: UINT): TDriveType;
begin
  Result := dtUnknown;
  case Value of
    1: Result := dtNoRootDir;
    2: Result := dtRemovable;
    3: Result := dtFixed;
    4: Result := dtRemote;
    5: Result := dtCDROM;
    6: Result := dtRAMDisk;
  end;
end;

...
if (Filter = []) or (IntToDriveType(GetDriveType(DriveRoot)) in Filter) then
...