Most modern electronic devices have adapters that accomodate electrical systems in North America, Japan and the UK. I think NA is 120v, Japan is 110v, and the UK is 220v or something like that. If you read the fine print that's stamped onto the back of the adapter it will tell you its acceptable 'range' of usage. Last I checked my laptop was good for multiple regions.
Speaking from ancient experience with the original Nintendo/Famicon and SNES/Super-Famicon systems, you will need some kind of adapter, chip, etc., to play games from Japan on your North American market systems. The games are not interchanagle as far as I know, and it's not the games its a firmware issue with the consoles themselves. Many people here as I'm sure you know get their consoles chipped (actually I had my old Playstation 1 chipped), thus allowing them to play burned and foreign games.
Buying a laptop before you go to Japan is well-advised. They have lots of goodies over there but getting a laptop with an English version of the OS installed is not as easy as you'd think. Also, if you go with a large manufacturer like Lenovo for example, worldwide warranty coverage is provided. My understanding from two of my friends who bought laptops abroad is that in order to have your warranty honoured you're often required to send the unit in and it takes 4-6 weeks. The warranty is usually only good for a year. For Toshiba machines (one of the most popular brands in Japan) you must take the machine to the place of purchase, you cannot take it directly to Toshiba.
My Z60m Thinkpad worked fine in Japan, the adapter that came with it charged it properly and I didn't have any issues. I also had intn'l coverage (on-site) for repairs which was a good piece of mind while I was abroad. Maybe you'd like to check into what plans come with whatever laptop you're buying.
Again, if you plan on buying any peripherals that require software, like DVD burners, external storage units, etc., your best bet is to buy that stuff at home. I was interested in an external burner while I was there and I was told it'd be incompatible with my system. Non-software peripherals like speakers will work though.