Both Lazarus and I are doing comp sci at unsw.. there was somebody else too, I *think*?
Anyway, the first year is maths + computing and four electives (unless you get the co-op scholarship, in which case it's two electives). As Bon said, being good at (and enjoying) maths is a bonus, but not essential.
Comp Sci is probably the most general of computer related degrees (the others are engineering and IT.. the former is quite focussed and can be difficult, and the latter focusses on different areas, i believe...) which is why I chose it.