If you're doing extension at Monash, I think it's called MUEP; if it's at Melbourne Uni, it's UMEP
For UMEP Biology, I think the pre-requisite is Biology 3/4 in Year 11 with a minimum of 40 SS (although I think they make exceptions if you have good recommendations and good grades in other subjects); otherwise, the alternative is doing Biology 3/4 alongside UMEP Biology in Year 12 (but obviously, again, you need good recommendations and good grades in Y11 Biology and in other subjects)
You're right about grading: if you get 90+ average for the 2 semesters=5.0; 80-89=4.5...
t35t and I talked about UMEP (Biology in particular) in here:
Why should I do UMEP?You might also find this useful (although you probably could have found this yourself online :p):
http://futurestudents.unimelb.edu.au/__data/assets/pdf_file/0004/486355/2012_UMEP_FINAL.pdfJust ask if you have any more questions!