Just install a Japanese input language, and make sure to place a tick beside Microsoft IME. Switch to Japanese layout, as needed, and make sure the IME setting is set to Hiragana. You can try other settings from there, just saying which worked for me.
Works everywhere - notepad, Word etc., including in TextBox inside VB.NET application - you don't need to change IMEMode of the control.
To add an input language in Windows 7, go to:
- Region and Language -> Keyboards and Languages -> Change Keyboards -> Add