There is so many factors that it could be. Nothing is a quick easy fix unless you have spam that can be removed.
A 64 mb video card should be stream video just fine at native resolution. To test out your hardware just put in a DVD or something and see how that looks. When watching the DVD if everything is fine then it is not your hardware, errr, your video hardware that is the issue. The problem lies somewhere between the source and your network card. Although when streaming there are other factors like browser, software, OS, RAM, etc.. I would suspect your connection first and to test this out do a speed test.
HERE (not sure how this works overseas) If you are "streaming" videos then I would think that you would need around 1.5 mb down for a smooth flow. If it's high quality you will probably need a bit more.
Clear up any spam that could be taking up bandwidth.
You should probably have at least 1-1.5 gigs of RAM, recommended 2.
Running IE7 with all the patches and fixes.
If I was streaming, I would be plugged directly into the cable, no wireless. Streaming wireless can be pretty crappy if you are running it over a crappy network card.
It could just be the source. MOTOGP.com has a crappy pipe out.