It should work fine. It just goes by the current language settings on Windows, not internally, to my knowledge, so if you're playing in windowed mode, just keep the language toolbar in the taskbar so you can see what mode you're in.
Alt+Shift will switch languages between EN and JP, but by default, Japanese mode is still alphanumeric. From there you need to manually switch to hiragana/katakana with these keyboard shortcuts:
Hiragana = Ctrl+Caps Lock
Katakana = Alt+Caps (note that if you just switched to JP input, this will actually activate hiragana mode first; from then on it will only activate katakana, and you'll need to use Ctrl+Caps to switch back to hiragana)
Alphanumeric = Shift+Caps
Also, Alt+` will toggle back and forth between alphanumeric and whichever kana mode you used last (semi-redundant, but it's designed to emulate a Japanese keyboard, which has dedicated keys for this type of switching). All of these shortcuts are customizable in the language settings.
Edited, Oct 5th 2010 1:14pm by TraumaFox