PHP e-commerce questions

Hello. I have built a site where people can register their weddings. I use MySQL/PHP to handle the database. I wish to add a step where people must pay to enter their information into the database. How do I do this? What services do ya'll recommend? I won't need a complicated shopping cart, since there will just be one thing to purchase... I just need something that takes credit card information and then assigns the user a username and password... thanks a lot, Matt --