E.D.
Are you trying to download using the ipod itself, or through the computer program itunes? If the ipod is plugged into the computer, you will not be able to use it (it's screen is disabled until it's unplugged again). You download through the program.
This link might help. It shows a video. Good luck!
http://www.youtube.com/watch?v=EMPES4C6hLY
http://www.youtube.com/watch?v=thC4uYl7TNo&feature=fvw