Congratulations on finishing the HSC and for getting such excellent results!
Bachelor of Computer science and technology (advanced) could mean a number of things.
See this website
http://intranet.eng.usyd.edu.au:8000/cgi-bin/show_plan?=BCSTCS--&
In the table, you will see subjects in blue and subjects in black.
the ones in black are non specific.
This means for Maths there might be 3 levels - fundamentals, normal, advanced.
You will by default get into the advanced stream.
Secondly, if you look down the bottom of that page in the notes, in point 4 you will see:
"Through this table, candidates may substitute an advanced equivalent for a non- advanced unit mentioned. They may also substitute an appropriate unit from the Advanced Engineering program of the Faculty of Engineering, or the Talented Student Program of the Faculty of Science, if they are eligible to enrol in such units."
THis means that if the Dean of engineering or the Dean of Science invites you to join the Advanced engineering program or the TSP, then you will get to skip those black subjects altogether! and do units in the Adv Eng or TSP!!
Advanced is pretty cool. I have a few friends doing it. it simply means you get into groups and work on research projects. So perhaps helping with someone's PhD or finding the cure to cancer or researching energy efficiency or the like. Very cool.
I cannot tell you the career prospects because i cannot predict the future!!
But anything computer science is doing well at the moment and i don't see why it will slow down.
Although it is best to speak to someone who is currently studying or recently graduated from that. You can probably find one at Sydney Uni Info Day on the 6th Jan.