Alt + Caps Lock -> Katakana
Ctrl + Caps Lock -> Hiragana
Either qualifer key is fine (left/right both work). Note that they don't toggle--they just switch to that specific mode.
You gave me a nice pice of information there. I really pi$$ed me off a LOT to use the mouse to choose hiragana after changing to japanese mode. I still don't understand why roman alphabet is by default instead of hiragana, a behaviour that can't be changed.
You made my life easier, thanks!.