Does this problem occur when you try to open multiple video tabs simultaneously?
If yes, then it is bound to slow down a bit.
Also, if you are downloading some files while watching the video, then too, the speed will be comparatively less.
Also, considering that you are using your laptop, check your signal strength, may be it might be weak where you are sitting.
Sit in the room closer to the router, which can offer better signal strength.
If you use IE, then I would suggest you to switch over to Mozilla Firefox 3.5. It is much faster compared to IE.
Hope I could help!!!