Modify Tax behavior in Oscommerce - Again

Our company is located in Sweden. All sales to Eu shall be with 25% VAT. Our company has a daughter company in Germany. All sales to Germany should be with 19% VAT. Sales to countries outside EU shall be without VAT. The system works fine if the customer has created an account and registered his/her country then the system displays the correct VAT. What we need is to make the system displays the correct VAT even so the customer has not created an account. This should be by letting the customer choose his location at the very first page of the website.