The undergraduate system at Melbourne works such that students undertake a "general" degree. Once the Melbourne Model is fully implemented there will be 6 degrees to choose from.
Arts
Science
Commerce
Biomedicine
Environments
Music
There are still some other undergrad courses available because the Melbourne Model isnt fully implemented yet but once it is fully implemented there will only be 6 undergraduate courses to choose from.
Courses such as Law will be moved to postgraduate studies.
If you wish to study an undergraduate degree at Melbourne and then apply to study the Juris Doctor then you will need at least 6 years of study (3 years for undergrad degree and 3 for Juris Doctor).
As for an ideal undergraduate course to lead up to the Juris Doctor, I guess Commerce or Arts would probably be the most common once the system is underway.
Something like 50% of Juris Doctor positions will be CSP so you risk studying 3 years of an undergrad degree and
1. Not being accepted into the Juris Doctor
2. Being accepted on a full-fee place
For this reason a large amount of potential law students have chosen to study at Monash because the Law degree at Monash has been retained at undergraduate level while the Melbourne law degree has been moved to a post graduate level.
To be considred for a position in the Juris Doctor you must also sit the LSAT test.
http://coursesearch.unimelb.edu.au/coursedetail.aspx?cid=884&er=1&ctype=1Ultimately I guess there are no guarentees but if you are really determined then you have a chance of studying the Juris Doctor if you persevere.
Alternatively you can go to another institution where the ENTER isn't so high, and you will be able to study law at an undergraduate level (also less time frame required to complete the course and be qualified to practise as a lawyer).
Hope that helps