Although Panther has a preferences pane called Internet (in /System -> Library -> PreferencePanes), it is an alias to the .Mac preferences pane. So I replaced the alias with the Internet preferences pane from Jaguar (10.2.3), and it worked -- when I opened System preferences, I was presented with the familiar Internet icon.
You can login as root user to replace the file. Alternatively, since I had a dual boot eMac, I booted into OS 9, replaced the file, rebooted under OS X, double-clicked the new Internet preferences pane, and the system asked if I wanted to install the pane. I replied yes, and that was it!
[robg adds: I do not recommend replacing bits of the system with bits from prior versions; it seems like a recipe for potential future issues. If I were going to try this, though, I'd recommend trying to add it as an 'extra' user-installed preference pane in ~/Library -> PreferencePanes, not in the top-level System folder. That way, you won't be modifying the system itself, and the hint should still work as described. If someone does test it in this alternative manner, please post your experiences.]

