Ok, i shouldn’t have got all cocky about it. The upgrade went fine, apart from the bootloader (LILO). Everything was working, but took a long time. Last check last night was a reboot, and LILO failed to boot the kernel. As this was 23:45, things have been down until i fixed it.

The fix is to create a boot floppy from the other debian box, boot from that, then reload the boot loader. All seems well. I have no idea why the bootloader failed.