[polka-dot-jewel]

I'm actually doing a lot of research for Japan, also. (I plan on going to both Yokohama concerts, too!) As of right now, I won't be staying in Yokohama, but I'll be staying in Asakusa. Here's a website for a hostel that's in Yokohama:

http://yokohama.hostelvillage.com/en/

Well, there's two airports in Tokyo - Narita and Haneda. Narita handles all international flights, so I bet the site you used figured you would be landing there and you'd find your own other transportation to Yokohama. Also, I'm pretty sure Harajuku is about 20-30 minutes away from Tokyo.

Hope all this helped you some more! =)

EDIT: And Hatix beat me to saying all of this. =P