After two years (IIRC) on a 457, you can apply for a permanent visa, and that's also easier - and more expensive, of course - with a nominating employer. At least at the moment, there doesn't seem to be any education requirement for the nominated permanent visa (but they have a tendency to change the rules quite often).
The 457 requires you "have skills, qualifications, experience and an employment background which match those required for the position". I never finished uni and got a 457 in 2008 (I'm Swedish). I did have ~10 years of experience though.
The Department of Immigration have lots of information on their site, http://www.immi.gov.au/.