If you REALLY want to be a mechanic (and think about it long and hard, cos its not for everyone!) then getting a job at a small independant place is the best place to start. You learn so much more then at a dealership. My first job on my very first day was helping a tech do a head on a Nissan S-Cargo! You get experience in a vast variety of cars, and learn just how shit Holdens really are! I worked at a small place in Malaga for a year, now work for Mazda. Mazda is great, much easier, but you dont learn as much as I did when I worked in Malaga.
Having said that, as soon as I'm qualified I'm getting the f**k out of there cos I HATE this industry! But like I said before, if you're made for it, then its a great career. I work with a few blokes who I know will work as a mechanic for years and years, yet at least 50% of my tafe class will quit within the first 5 years.
Finally, you dont want to start out at a performance workshop. Think a normal mechanic workshop is stressful? Performance is soooooo much worse...