This was not as easy as it should have been. The media check failed, (erroneously I believe, as the sha1sum checked out), and then the graphical install wouldn’t work. I managed to get X running by fiddling with /etc/xorg.conf (the trick, if you need it, is to insert the line in the monitor section Option "UseFBDev" "true" and to comment out the horizontal and vertical sync – this doesn’t actually solve the problem, but it allows system-config-display to run and you can then input the correct details). Still, the fact it works is satisfying, even if I have still to get my Airport card configured…