I found this article invaluable and helpful. It explains how to make a standard Japanese keyboard work with English Windows XP. Note that the solution described still allows you to switch quickly to a US or UK layout if you're more comfortable touch typing that way.
http://www.kurnspatrick.com/keyboardmapping.htm
You must be careful to follow the instructions exactly, even when they seem counter-intuitive. Since you are bypassing Windows defaults, you'll get a couple of scary sounding dialogs which you can ignore.
I was so pleased that the keys now match the keycaps on my wireless keyboard.