I did used this site, and I think it works...
There is an option of North America and Europe. (You need to choose where you bought from). I did bought from Europe so click that one. The next page will be asking you about your date of birth and country. After that on the left hand side Click the 'Qualifying Products' to see, if you have the correct product (In this case i bought HD 6950 so its good to go) then click 'Claim Form'
Fill the form, serial number is on your product box, after submitting they will ask about proof of purchase so you need to give them a screenshot about your product purchase (If you did order online, your retailer must have a website and if you log in that website you can also find the info about your order shipment, screenshot that). Then attach it to your mail that you want to send (in this case, they would tell you which email you should send).
Wait for few days of confirmation and VoilÃ*..