Music videos show on song lists, I guess the rationale is that music videos are songs too. The only way to exclude them is to:
(1) Change the video type so something else ▲,
or
(2) Alter your playlists to exclude video files. Since you are still using iTunes 6, the easiest method is to create a playlist for all video files (dynamic or manual), then add a line to your other playlsts to exclude any item that is in the new video playlist.