strange network problem with Knoppix v5.0.1 on IBM T42p

I installed the new version of knoppix on the IBM T42p laptop. Everything is fine except the network. The strange thing is that it can browse the network with a quite fast speed. But it cannot really download the file. It is always stalled at the beginning. I try to use wget command to fetch file. It results that each time it has a burst speed (~200k/sec) at the beginning for a few seconds then fading to zero shortly. What might cause this problem? Thanks a lot!