Looks like the total wipedown & reinstall of the OS on the powerbook worked: complex 3D no longer causes the system to go all pear-shaped. As something of a bonus, I was able to trick the OS installer into restoring all of my user files & preferences from my backed-up system. The only stuff it didn’t grab were the UNIX specific things that I’d installed.
Here’s a handy tip for folks who need to do a backup and reinstall under Mac OS X 10.4: use Carbon Copy Cloner to make a clone of your system to an external hard drive. Then, when the Tiger installer asks if you want to transfer data from an older Mac, just say “Yes.” Hook up the external drive when it prompts you to connect the firewire cable to the older computer, and it’ll do the rest. Saves a ton of time on reinstalling and reconfiguring OS X applications and users.
Of course, this does you no good if the problem with your system was a screwy configuration file. And it won’t transfer anything you may have done with the base BSD system.
In my case I had installers all ready to go for most of the UNIX stuff. The Apache2, PHP5 and SVN batch installer I did up a couple months ago worked like a charm, and the MySQL installer from Apple’s website was fine too. The only kind of tricky thing is going to be getting my local install of PHP wiki back. Not so much getting the program itself up and running, but getting all of the data out of the old version of the wiki and into the new one without screwing up any of the database tables that it’s stored in.