For the cleaning, you have a few options:
- carpet cleaners: there are products sold to clean carpets and upholstery. Some are liquid based, some are foam based (you spray them on), and there are even simple home recipes like baking soda. Basically, treat this like you would a stain on a carpet in your home.
- heavy duty cleaner: I don't know about Australia, but here in Canada you can rent a carpet cleaning machine for rather cheap. They are electric and use a solvent. Most are rather cumbersome and meant to be wheeled over a carpet, but many have small nozzle attachements that you can maneuver around a car
- automotive detailers: you can have the interior of your car shampooed professionally
For the vents, take them apart and clean them with regular soap and water. The key is to taking them apart. Make and model could help us find more specific instructions.
Once all the material has been cleaned up, getting rid of the smell is a simple matter of airing out the car (drive around with the windows down), and use some room freshners. I never use car freshners, mostly because I don't like the fragrances available, I just use the jelly-stick room freshners. There are also spray products that kill smells, they are generally advertized for couches and drapes