You should have already pre-enrolled for 2006. At the moment, the university is just cross-checking the pre and co-requisites for what you've said you'd like to do with the compatbility on your course.
Once this is complete, they'll send out a confirmation of enrollment letter to the address that you have listed in Student Self-Administration, plus an invoice for your HECS/Fees. This means that you are enrolled for this year.
At the moment, the anticipated time for this letter is for sometime in the next week (week commencing 23rd January) Payment or deferral for the HECS/Fees is expected to be around the 6th - 10th of February, depending on when they get the information to us.