Mate, technically I don't think you need anything but I'd highly highly highly recommend at least 2unit maths. 3 or 4 unit maths will help you alot in first year.
Phys would help a little bit (moreso than chem/bio but is not that neccesary if you put in a bit of effort).
Chem/Bio a bit pointless (it won't help that much in biomech) but if you are interested in biomech you naturally should be looking at doing them anyway right?
Last year the main round uai (straight science) was 73 so this year around that.
Now the bad news:
I transfered to science combined to do biomech but a 2nd level compulsory course was cancelled in session 1 of this year.
I emailed the lecturer back in Feb and got this:
thanks for your email. There have been some major changes with programs at UNSW which have made 2451 and 3451 appear to be unviable due to small student numbers. I will be speaking to people within the Science faculty to assess whether the major and minor are continued, or if there is a way of offering those courses every second year, for example. I should know the status for 2007 of the courses and the major and minor by the middle of 2006.
Best wishes,
Andrew McIntosh
'2451' being the 2nd level course I need.. So I'm not even sure if the major is available for next year? (I've since dropped science)
Biomech seems to be unavailable on the 2007 handbook:
http://www.handbook.unsw.edu.au/undergraduate/programs/2007/3970.html
(just as a minor) So I'm not really sure what's happening with it
All the best