Japanese keyboard map in Windows XP

I decided to install a WinXP partition on my desktop machine which usually runs Linux, to avoid booting my laptop all the time to play ren'ai games. My desktop machine has a Japanese keyboard - I bought it for the heck of it when I spilt coffee on my old one, because I thought typing directly in kana would be fun :)

In Linux, I just selected Japanese keymap, and everything worked - all punctuation was in the right place, hankaku/zenkaku, muhenkan, henkan, etc.

In windows, I set up my keyboard as being Japanese, and e.g. if I select the KANA button in the language bar pressing the keys yields the correct katakana character, but that's about as far as the functionality goes...
None of the special keys work (hankaku/zenkaku just prints a backtick, the others do nothing at all), and the punctuation is as if I was using a US keymap.
The punctuation is the main annoyance, seeing as that even affects me in English mode (which is most of the time), and I never learned to touch-type on an American keymap (I usually use British).

Anyone come across this problem and know how to solve it?