You sign up online and then just present your card that you receive in the mail when you check in. (If you don't receive the card in time you can print off the membership number that you receive in your email.) As far as renting a car - it depends how much you plan to spend on food/drink at the hotel. Depending on traffic, it's about 30 minutes to an hour to the resort. There is nothing really within walking distance once you get there. The resort has everything you would need but their prices are very high (bottle of water 4.50, mixed drinks 10, breakfast buffet 20, etc). Depending on the cost of a rental, it might be worth it to rent a car - you can also drive yourself to some excursions (like the rainforest) but also keep in mind they charge $15 per day for parking :).