seriously though do you have other programmes running? internet streaming can be pretty resource hungry so if your pc is working hard it might struggle. also check any firewalls you have arent interfering. check the media player you have to see if you can raise the buffering level and check the connection speed is correct. also, if the site your streaming from opens in a browser window see if you can open it without any flash on and see if you can change the connection quality.
meant to say, try changing the media player your using. windows media player is ok but winamp or VLC are both better.