So, I think I fixed Wacky Leopard Bug #2, or, at least, the symptoms of it. The fix turned out to be simpler than I expected, as I simply had to reset the Keychain according to Apple’s instructions. Honestly, I’m not sure what this did or why the old keychain wouldn’t work, but in this situation, it’s not a big deal: there were few to no passwords saved on the computer. However, it is pretty strange to me that this situation happened during the bog-simple upgrade of the powerbook, which was running a virtually clean install of 10.4.10 before the upgrade.