Well, according to PC web, the only step I was missing (after all the stuff in the two previoius posts) was to turn off the “Escape non-ASCII sequences” option the Emulation section of Terminal.app’s “Window Settings’ dialog.
Terminal.app has this clever feature, where if you start inserting Japanese into the terminal, it displays the pre-edit buffer inline, and shifts characters that are to the right of the cursor position to the right temporarily, without telling the application in the terminal anything. This works surprisingly well, almost to the point where I don’t understand why this hasn’t become the convention.
On a related note, the pcweb site linked above has a ongoing column called OSX hacking, so I plan to read through all that and report back. It’s like MacOSX Hints, but in Japanese, I guess. He spends several columns to explore various settings for CarbonEmacs, which I guess I’d like to try out at some point.