Distortion on playback

[2thman]

I know this problem has been around. When I play an flv file that was saved using download helper. Distortion begins to develop in the face of the person in the video. When the distortion gets really severe the image snaps back to normal and begins to distort again. There is another site that speaks directly to these symptoms http://www.kmplayer.com/forums/showthread.php?t=8338 I just don't know how it relates to me. What is interesting is that this does not occur on all downloads. I have a imac g5 1 gig memory, using Firefox 3.0.1, vlc 0.8.6i . I am downloading an flv file off of a MyFox TV site. Thank you
2thman