Make sure you have the latest version of DXTBmp.
http://www.mnwright.btinternet.co.uk/index.htm
This should automatically create the Mips when you save in an Extended BMP format.

Some people have found that removing the Mips makes the textures sharper. This might depend on the aircraft or your videocard. You can disable Mips when you first run DXTBmp (Uncheck Include Mips from DXTBmp/Prefs.) It will return to the default "Include Mips" next time you run it.