Automatic membership of Japanese site.?

I was accidently linked from a particular site to a Japanese website. Out of curosity, I decided to click on one of the videos and a msg in Japanese prompt me to enter the site.As my Japanese is rather limited, I click "enter"without thinking twice. It was then I was linked to page where my IP address and a msg saying that "my registration for membership is successful" are shown . I was provided with an user ID and was asked to pay membership within 2 days via mail (ya I was provided with the company address). How come my registration go through when i didn't even provide my personal particulars such as my email/home address/credit no.? I find it really fishy so I went back to the previous page to check the terms and conditions. I read that there is one term which says that if I don't mail out my fees within 2 day, I will be responsible for some additional fees(not sure what kind of fees since my Japanese is rather limited).. So will the company able to track me and demand me to pay the bill if they only have my IP address? I'm not from Japan and I don't even intend to sign up for any membership but this worries me..