I just took my first steps into Windows Media Services but I have some problems with the buffering of the stream.

I send from Expression Encoder 2 SP1 to my publishing point on my Windows Media Server. But when the quality of the video is too high, I get some buffering problems when I'm watching the streamed video with my Windows Media Player. After looking 5 seconds to the stream, the windows media player stops with playing and in the left bottom corner I see the text "buffering". After 3 seconds buffering, the player goes further for a next of 5 seconds of playing and it continously does this.

Somebody knows what the problem is ?