Have just restored this morning's SuperDuper backup..
I did what you suggested in the last paragraph, checked the 10.5.2 Combo sha was ok before using it. Dropped the package onto Pacifist, ran verify first, and was surprised 300+ of my files had the wrong checksum.. (did my original 10.5.2 update go wrong?), anyway I went ahead with the install, accepted a bunch of things underway(?), and restarted.
It booted ok, but I quickly went mad with GoogleDesktop agent repeatedly wanting to 'relaunch,ignore or report', none of which helped, and I couldn't kill the process, grrr! The same with iChat, likewise ClamXav, and I decided things weren't so bad before after all - VINE viewer screen shares with no problem 😉
I'll wait for 10.5.3.. thanks for your help though Ralph.