Pretty much the only courses you will get out of TAFE will be courses that will help giving you certificates to get you into the animal care, zoo keeping or veterinary industries.
I'm not sure where your located, but for NSW (particularly sydney) you could start of by doing a Reptile and Amphibian care course which then leads into the Advanced reptile and Amphibian care course which is broken up into 3 parts
1) Advanced reptile - python, lizard and turtle care.
2) Advanced reptile - Venomous snakes and crocodile care
3) Advanced reptile - field surveys
To get into the advanced python, lizard and turtle course you have to have completed the reptile and amphibian care course, and then to get into the venomous snake and crocodile care you have to have completed the advanced python, lizard and turtle care etc etc. It all goes in order and you can't necessarily skip one of the steps.
Also, you could do a certificate II in animal studies. This course has 2 strands to it, Companion animals strand and Vet nursing strand. The 2 courses are basically the same up until semester 2 which is when they start to teach you about either vet nursing or companion animals(obviously depends on which course you are in). So if you chose to do the Cert II in animal studies, companion animals strand... you would then have the choice of doing Cert III in captive animals the following year, Cert III in companion animals or any of the other Cert III courses that come from completing Cert II in animal studies - companion animals strand. If that makes sense. The difference between Cert III in captive animals and Cert III in companion animals is that captive animals is more for the zoo type/animal park industry (caring for wild animals in a captive environment) which companion animals could lead into a career like RSPCA officer, dog Kennel carer or whatever...
If you want anymore info on the TAFE courses send me a PM or an e-mail as I am in the middle of completing all of the above.
As for actually doing herpetology at uni, pretty much the only thing you can do to prepare yourself for it is do biology in your HSC and be very good at it. As for info on uni courses and what way you have to go to become a herpetologist you would have to speak to someone who either teaches it or is currently in the middle of doing it (I'm pretty sure there are a few of both getting around on this forum). But be prepared for a few years of study at uni if you do choose to do herpetology.
Obviously while doing all of this it would be a good idea to volunteer at a zoo or animal park. And if your able to get a job at one, then even better.
Cheers,
Kane.