Of course Japan are in the World Cup...and in a shameless bit of self-promotion, if you want to read about the Japanese national team and what they are up to have a look at my Japan blog on the World Cup Blog site
Japan World Cup Team Blog leave comments, discussions and so on, or just get to know more about the Japanese national team.
As for the Japanese league, well baseball is the number one sport I think, but football is right there too. The new J-League season starts next weekend (first weekend in March), and of course many of the players will be hoping to grab a spot in the World Cup squad. Having lived in Shimizu (Shizuoka Prefecture) I am completely biased in favour of Shimizu S-Pulse, and utterly biased against Jubilo Iwata. Gambatte S-Pulse!!!