How to buy Sony ebooks outside the US
Just tried it, your reader software must set up to English / North America.
For your credit card information it's enough to insert your real address. Just modifiy the ZIP and the the state (for instance WA). If you don't have a real ZIP search one with 'yellow pages' (would be nice to use Amazon's ZIP *hehe*).
The credit card is from Germany - so no problem.