How do I obtain a title in the state of Texas?

I've got a nice car, and bought it without a title. It was an extremely good deal, and I got the bill of sale. The person I bought it from lost the title from when they bought it from the original owner. Problem is, is that they never got it transferred from the original owner's name. How can I get a title from the state of Texas for this car?? I have a signed and dated bill of sale, and all I need is the title. I plan on going to the courthouse tomorrow. Any suggestions??