your specs are quite slow, I'm guesing its your processor, I'm using a intel celeron 900mhz, 256mb ram, and intel intigrated graphics and videos run fine, so thats why I think its your processor, what about the other computer in your sig will the videos play on that?
Just tried the video and it lags a bit on mine so could be their web server. I will try it on my laptop (which is more powerful) tomorrow and see how it plays.