Right, tried it with a dozen and still the same. My method seems OK (or at least I've done the same thing wrong twice).
So the next logical thing must be perhaps the font files aren't all they should be.
I'll try it with some different ones when I have time.
Thanks for the replies anyway guys.
ps last time I plugged into the USB and turned it on, the cybook froze at the first of the screens (with Clinton's book), so now I know the reset button works too