Jobs I want my sim to take the Movie Star career track but it never shows up when I do find a Job. Do they have to graduate from collage to get it?
None of the new careers are available unless the Sim is a college graduate. And there isn't a way for any Sim who is already an adult to go back to college to get that necessary degree. It's a bummer (although I can see why Maxis didn't put that in. They wanted the young adults to be special. It really changes the character of a university if it is full of adults as well.)
read through your "declare major" options. each one gives you at least 3 career tracts that the major is suitable for. some are better than others.
The only reason to choose a certain major over another is the types of skills required to pass the semesters. You can tell what skills the majors will focus on by looking at the bottom of the window where you select the different majors (that also shows what careers are good for which major as Michelle pointed out). But, if you're like most players, by the time you get your teen into college they are far beyond any of the skill requirements.