As far as the U.S. is concerned, the requirements vary from state to state. There's a site with links to the various state regulatory bodies on ECN somewhere -- Perhaps one of the U.S. members could post it?
Visa/immigration issues will also be a consideration. As somebody who has jumped through all the INS hoops to get work authorization in the U.S., I can assure you that a plentiful supply of patience is definitely a requirement!
