When streaming videos, why can't I skip to different parts of video in QT? Its like it won't buffer enough of the vid to even play without pausing....

Can anyone tell me why when watching a movie with qt streaming..... Why it constantly pauses my movie to buffer and won't let me skip forward to another part of movie but instead starts the movie at the beginning again? Do I need to upgrade to something else? I have a cable internet connection and it works when using realplayer, for example, but with quicktime it *****. I've tried to look in preferences but can't find a solution to the buffering speed or anything..... any help out there???