I've used Priceline with a MasterCard and Visa, following the exact instructions from Bidding for Travel. Besides the "California" business, I've noted that for "ZIP code" you should use five digits - 99999 works for me. You should familiarize yourself with the guidelines presented on that board - they work and there are many useful tips. Just remember if you post anything the administrator will correct you quickly and scold you if necessary (Pretend you love the criticism and it won't hurt.)