Do I need to register with BMI or ASCAP? what does it mean exactly?

No, there's no annual fee for BMI (and I don't think there's one for ASCAP) -- BMI is a nonprofit and the money they get comes from money that otherwise would go to you, if you were going to get any money. (So, they broker a contract with a club for $100/yr or whatever, and $95 of that is split among artists and $5 is kept by BMI, if I understand it right. The numbers here are totally ficticious.)

If I could just figure out how to tell BMI I've moved so I could get their sparkly newsletter again then my life would be complete.