One other option you may want to explore is making a partition on your hard drive and then installing a Japanese operating system on that new partition.
I use Partition Magic V.6, dividing my hard drive in half. This allows you to install another operating system (such as Japanese Windows 98). The program also includes Boot magic. This allows you to switch between the different operating systems you have on your computer when first booting up. I choose from Windows ME or Japanese Windows 98. You can install Japanese-based programs on the Japanese partition (have Japanese Office Professional, and Japanese Microsoft Explorer for internet stuff).
These programs enable you to make the changes to your hard drive without using the famous "format C:" to set up partitions. Partition sizes can be changed or altered easily at any time too.
Using a Japanese operating system will solve any problems that the Microsoft Japanese IME will not translate.
I hope this helps,
Dana