So, with the CM7 kernel, moboot loader and CWM recovery, there is not enough space in /boot for the kernel installer (on my system anyway) to shuffle the files around to do a kernel install.
I had to log into the TouchPad using Novacom, move the /boot/update-uImage file to /media/internal, then install the new kernel and and move the file back to /boot.
I've got a grand total of 16Kb available in /boot, it starts cleanly though so looks like I'm ok.