This is very good considering that you have to pay and buy at least a 5 user pack which costs like $100/year (or less if you order clicking the banner on the left side).
Anyway, to get your free full 1 year license just visit their BitDefender Promotion for Australia section and enter your details to receive your license through email. If you have an evaluation version already installed just click on the ‘General’ button on the left-hand side of screen and click on the ‘Registration’ button. Click on ‘Enter new key’ and type in the serial number to register the program. And that's it, you have it registered.
If you don't have an evaluation version, you can download by visiting their Evaluation Versions section and choosing BitDefender Client Standard v8.
In case this promotion ends, they also have a free edition you can download directly using this link: BitDefender 8 Free Edition
To see a list with the differences between the editions they offer (BitDefender 8 SpamDeny, BitDefender Client Professional Plus v8, BitDefender Client Standard v8 and BitDefender 8 Free Edition), just click on the image below to enlarge it: