if you are eligible to become a citizen and u are not, u are still eligible for hecs, but u need to pay ur tuition fee upfront, and not eligible for the 25% (i think changed to 20%from 2004) discount when payin upfront...
so yea, get ur citizen ship before enrollment... even with the letter which certifies ur citizenship has bein approve makes u eligible to defer... or discount for th at matter...