Assuming that you're using Windows XPee, it's not the browser at all, it's a component of the OS. Go into the Regional Options applet of the Control Panel, and under "Language Settings for the System," check the Japanese checkbox. Insert your XP CD when prompted, and it should install Japanese language support.


(Note: I just spouted that out from memory, and I have probably forgotten a step, so just post any problems you have with that solution)