Yes, that's correct... One Pro Card at the North Americans, to the Overall winner. All class winners get Pro Cards at Nationals.
One of the reasons that I want to try to do the NA's is because it's been a relatively small show for the lighter weight classes in recent years, and it's a Pro Qualifier. In 2007, there were only two LWs. In 2006, there was only one LW, so she showed up to compete and was automatically in the Overall competition for a Pro Card!
As of right now, I haven't heard of any other LWs doing the NA's, but there will probably be some. I know two MWs, one LHW, and one HW who are all doing it (one of them is Melissa Detwiller!). The Mexican BBs always make a strong showing at the NA's too, but they are usually pretty big girls. Assuming I could make the LWs, it could be a good opportunity for me. But you never really know who's gonna show up until you get there!
P.S. Thanks Bernie and Judge. And thanks also tigereyes... I really hope we meet in person at one of the shows this year! We keep missing each other!