When I try to watch TV shows off the web, or the high definition trailers off the Apple website, they freeze every few seconds. I have a cable modem, so I don't think the problem is bandwidth. Could it be that I don't have enough RAM? I have 768MB. Or could it be that my four year old iMac doesn't have the graphics card necessary to process the video quickly enough? Any thoughts on what causes this? Incidentally, my two year old IBM ThinkPad does the same thing. Any suggestions on what I can do? Close other applications, etc?