It depends on what you are transfering. Short files do not take up as much bandwidth. When transfering large files over my 10mbit LAN, my utilization is 70% in the Task Manager (without any tweaks and QoS running).
It could also be due to the fact that you're on a P200MMX. It shouldn't really be so, but if the computer can't handle sending data that fast, be it limited by the processor, memory or bus speed. How are you measuring the bandwidth usage?
i just look it in the Task Managers network tab. I have tested with some program (don't remember the name) that my hdd is capable to transfer averagely 7MB/s, so the bottleneck isn't my hdd. the cable is 4m long, so it shouldn't lose that much of it's efficiency. i don't use a twisted pair cable, it's a BNC cable.
i tried transferring small files (about 4%) and a 400mb chunk (around 30%), and both machines' hdd:s are defragged just a couple of days ago.