get a laptop. Unless you think you can get along without one of your own, by using labs and stuff. It'd cost a ton to ship your current computer. And buying one there probably isn't the best option (although it may be cheaper, esp. for a nice Sony or something <drool> ) because of things like the keyboard being a Japanese keyboard, the OS and all of the programs that it comes with being in Japanese, etc... Unless you're so proficient in Japanese that you don't have any problem with that.
Also, look into the standards in Japan. Power may actually not be a big problem, since the Japanese took a lot of our standards after WWII. In Europe, they use 220V, but that wasn't a problem since my laptop power supply is dual voltage (I think most are), and I just had to get the appropriate plug adapter. But if you're going to try connecting it to an Ethernet network or use the modem, it would definitely be worthwhile for you to look into the appropriate adapters here, rather than get over there and not be able to hook your computer up, and have to spend time wandering the streets in a country where you have trouble with the language and you're looking for something obscure. I doubt that Ethernet is different, but phone plugs in Europe vary considerably. I have no idea what Japan has.
Hmm just checked out
Magellan's for info. It appears Japan uses 100V electricity. Magellan's sells both electrical and telephone adapters for Japan.