The disc that comes with the Japanese version would only have maps pertaining to Japan. The directions given would also be in Japanese so it would definitely be of not much use unless you were fluent in the language.
Sony showed the GPS in North America at one of the recent trade shows (CES 2008 in Las Vegas) but not much has been said since. They did say it is definitely coming to North America in 2008 but were not able to give a price or firm date at the time (likely not till fall/ holidays). The Japanese unit translates to about $51 US so I would hazard a guess at about $40-45 US here.