When i play videos on my DivX player, the playback is kind of jerky... Anyone have any ideas how to fix it?

I've got Vista (if that makes a difference) and the videos playback fine, the audio is fine but it just does a small jerk every second. It's like a video thats being paused and unpaused super quick all the time. It's watchable, but damn annoying. I downloaded the recommended bits and pieces, i didnt do a basic download, so can anyone tell me why it is jerking and how to fix it? Thanks!