[noodle]

It's quiete simple

Control Panel > Regional and Language Options > Keyboards and Languages > Change Keyboards > Add

Then you just add Japense... After, you do accept, ok etc etc etc... and at the bottom right, near your clock, there should be a little square that says EN atm, you click there and choose JP when you wanna use Japanese and if you wanna go back to english, just click there again and choose EN