I’ve shifted finally back over to the returned, repaired ThinkPad A31p. All’s well so far, and I managed to get by with (a) doing a mass copy of the Documents and Settings folder from the T40, and (b) not doing any big software upgrades on the T40 during this last stint.
Which now means that I can finally upgrade my Thunderbird and Firefox installations, rip the most recent CDs I got for Christmas, etc. Huzzah!
With luck, this will be the last time I need to do anything like this again for quite some time. Which deserves another huzzah!