Have answered some of your questions on another thread you posted on. Best to look at the DIMA website regarding student visas or call DIMA in DC with questions to get the definitive answers though. You can't migrate as an American w/o having a skill in a shortage area, so choose your Uni course carefully if migration is your end goal.
Hi Nina and welcome to the forum
Cannot personally answer your questions I'm afraid but here are a couple of links with more info -
Student Visa info - http://www.diac.gov.au/students/index.htm
General Links - http://www.adelaidebound.com/
May be worth you having a chat with a migration agent as they could fill you in on the terms etc of the different visas if you are unsure.