You don't have worry about the voltage, Japan uses the same as USA, as Mikhalia recommend don't buy your game copy until you are here, other wise you won't be able to purchase crysta with your Japanese credit card.
On the other hand if you are going to keep your American cards I urge you to purchase the game there, otherwise you will have the same problem but the other way around.
If you purchase a Japanese copy of the game, you would have to install the windows support for Asian languages (there is an excellent guide for XP here
) and consider buying a Japanese 106 key keyboard if you don't want to deal with a different layout.
Other than that, the game can be played in any of the four supported languages no matter which version you purchase, although you will need to get a Japanese SE account and the online interface be in Japanese as well (you can simple get a screen shot tutorial in English since the process is exactly the same)
I also recommend you avoid bringing any wireless devices, Japanese internet wireless frequency uses the same channel as some devices made in America.