Did you add the extra lines to the aircraft.cfg? Did you make an entry in your aircraft.txt file? Have you ever added textures before? Did you follow the instructions that came with the textures? Were the textures designed for the default plane?
Many many things could be wrong here. Could you tell us how you installed them, step by step. That way we can tell you where you went wrong at? Its an easy one minute fix, but we just have to know what to fix..
Sounds like you did not make the necessary changes to the aircraft.cfg file. If you follow the readme instructions you should not have any problems.