Thanks for the suggestions Arow. Just before I gave in to sleep last night I made a lot of progress on this and found your reply when I woke up this morning.
I found another post on here for a vaguely similar issue with Fedora; that suggested looking at boot levels. After playing about with it I found that I could boot to level two and then startx.
This then ran KDE, and my kernel mod had solved my touchpad issue.
I then rebooted and did interactive boot (I had completely forgotten this is possible, it's so long since I needed to do that). When it got to the touchpad part and asked if I wanted to start it, when I said yes, it went and installed some drivers from the installation DVD.
It boots happily now, which I guess is the main thing!