yeh, it's your global IP that needs to change - however, I suspect that it may be "cookied" or similar on your machine aswell, otherwise they would run into massive problems when people who share a NAT'ed internetconnection sign up. Think dorms and similar.

Either call them up, and ask for help or walk to a friends house and borrow his/her pc for 10 minutes. Library pc works aswell. In both cases, I'd suggest making these trial accounts with a bogus password, and then change it when you come home. At least then, you can be confident your didn't get hacked due to poor security-setup on the library or your friends pc.