It's not your university's GPA system that matters (as the scores are all converted to a common standard) but your performance in each subject as a percentage (ie marked out of 100) - this is usually referred to as the Weighted Average Mark.
The WAM is calculated by multiplying your mark in a subject by the number of credit points of that subject, adding the products of all subjects and dividing by the total number of credit points. In short this gives you your average mark out of 100 for all subjects, and is weighted to accomodate different subject loads (in the form of credit points). This assessment is used as a standard because just about all tertiary institutions issue a percentile mark (ie mark out of 100) as well as an academic award (HD, D etc). However, each university has their own system of determining the academic award: for example, at UTS an HD is anything worth 85% or more, but at UWA the HD is anything above 80%. So, a UTS student with a WAM of 83 will only have a distinction average but a UWA student with the same WAM will be considered a high distinction student.
Hmm... I've forgotten why I typed all that out. Guess it's time to get studying again!