Ok, just to fill you in. The way the installation worked is that it booted from the actuall downloaded iso file (not a burnt iso image) running from the XP root directory and using grub to dual boot.
As it happens I've just had to re-format my disk and re-install XP after everything got screwed up (that'll teach me not to lose my boot-disk).
I've now given up on that install option and I'm probably going to have to stop trying to use linux. I've tried setting up an internet connection from the above installation, from a regular knoppix-installer hard drive installation and while running from the live cd and I just haven't got anywhere.
I'm on dial-up and using an Intel 536EP data fax modem.
I have downloaded the correct linux drivers for the modem but I just can't get the driver installed. I have read of other people having problems with this modem and I'm yet to find an answer.
The first problem was that it wanted the kernel sources installed so I downloaded and installed those and tried installing again but this time it says I have an unknown distribution and it was unable to find boot scripts.
I tried Gentoo previously and had the identical problem.