Mexican food is yummy, cheese!?

I want to make Queso dip, the kind that you would order at a mexican restraunt, a little runny, white cheese based.. Really good.. :) Any ideas on the cheese? Or maybe a known recipe? And also! The white cheese mexican restraunts use on there tacos / soft tacos. What is it? Queso blanco or something else? If someone could enlighten me on that, I would appriciate it. Thanks!