Thanks for your replies. In one sense the problem is now over - because I found a fast ftp server and downloaded overnight and got the correct MD5.
But I'm curious about BitTorrent's not working. It works wonderfully well for everything except Knoppix.

The client I use is BitComet 0.70 and when I was trying to get the Knoppix DVD I did notice that no-one else was using this client.
They were mainly using Azureus or the official BitTorrent client.
Could that be relevant?
I don't suppose it is - but I'm grasping at straws in seeking understanding.

I accept what has been said regarding the advantages of BitTorrent - and would like to use it.
It doesn't seem likely that my set-up is to blame - in that it has worked perfectly both before and after my failure to get Knoppix.

Unless the Knoppix tracker makes different demands?
BitComet found lots of seeds and peers and connected to many of them and yet, even after fifteen minutes, was transferring data at a mere few bytes per second. It would have taken literally years at that rate!

I am now curious. What could affect Knoppix but not other transfers?