If you have any other debt, ignore this one, its the "cheapest" debt (in terms of the rate at which the interest compounds) you will ever have. Pay the other debt off first.

BUT (and I'm bucking the trend here) if you have no other debt, pay this off NOW while you have no other encumbrances because a) If you make voluntary payments you get a 10% discount and b) you can't predict how your circumstances will change. My sis has landed herself in a really tight position after she left her husband & started work, discovered she was really really good and got 3 promotions over 14 months, suddenly after paying little HECS the previous year she suddenly finds she is required to pay 10K on top of her regular tax...she has in that time bought a property and will not be able to make the payment. She is facing selling her home to fund the HELP debt because the ATO will show no mercy on the grounds of being a single parent. Even if you only pay off $500 a year then you reduce the likelihood of it coming back to bite you later.