A few other bits and pieces aren't the version I want them, in Python there are both 2.1 and 2.2 installed with 2.1 the "default", a python2.2-xml was compiled against some other minor version and won't install - is it wise for me to fetch the .tgz source for my Python things and configure;make them? Is this going to mess up the upgradabiity of my Knoppix, or is Knoppix perhaps such a hack that can't safely be "apt-get upgrade"d or "dist-upgrade"d?
I did apt-get update, followed by apt-get install python. As far as I can tell, the python version that I use by default is 2.2. I don't know what's wrong with your install, but when you did apt-get update, did it successfully retrieve package lists from all the mirrors? Or did some fail? If some did, try doing 'apt-get update' again.

For filesharing, the default sources do come up with lmule for an eMule lookalike, but no mldonkey etc could be found, nor do I see any Kazza options (as usual, I expect Kazaa to work under wine)
There is no KaZaa option under Linux. As for the other programs, you could always download them separately and install them. AFAIK, installing from source doesn't prevent distribution upgrades, which is cool.