Repossession!!!!?

About two years ago, I made the mistake of "being blinded by the sports car" when I decided to purchase a car. I went for a larger payment than I could afford on a Mazda RX-8, not to mention the gas on that car is ridiculous. I ended up voluntarily having it reposessed and took it to the bank myself. I know it doesnt help but it felt more honest that way. So I have two questions to pose to anyone who can answer. #1 How long will this effect my credit, I have been told 10 years but also other numbers as well. whats the right amount? Also what can I do to build it up if anything over that period of time? I know that I could pay the difference between the auction price and what I owed but the bank told me that they would be able to get the balance at auction and they didnt. I feel a little screwed over because they left me owing $10,000. The person who bought my super nice sports car payed as much for it as I payed for my Scion XB. SOOOOOO unfair. Tell me what you think.