Hi Stacey:
I do not think you actually have to join the Catholic Church in order to be married in it. I would talk to his priest about that. However, you can go through the Rite of Christian Initiation (RCIA) program which is a class that teaches you about the Catholic faith. That is the normal way someone joins the Catholic Church. I know some have taken the (RCIA) classes without actually joining so as to learn more about the faith and then they have gotten married in the Church. There are a variety of options opened to you. I sent you a private message with more info.
Jeff Schwehm