Does anyone know the old 20GB iPOD really well?

I have one of those old 20GB iPODs, and for some reason, I can’t seem to get it to load videos. Even if I try to put the correctly formatted (mp4) movies/shows, it never seems to load correctly into iTunes after I download it.
There have been a select few videos that work in my Quicktime Player, but so far, not a single video has loaded correctly onto iTunes, i only hear the soundtrack, but see no picture =/
Any suggestions?