There is no undergraduate law degree at the university of melbourne.
IF you really want to do law at Melbourne and are willing to get through 3 years of undergraduate study in another field, then you can apply for the Juris Doctor (postgraduate law at MElbourne). This degree is more on par with law degrees around the world which is why MElbourne did it. Very few universities in other countries do undergraduate law, but most in Australia do. Melbourne decided it would prefer to be similar to the rest of the world than the rest of Australia. What this all means is that if you do the juris Doctor after a bachelor degree, you will have a law degree which will be recognised internationally, which most undergraduate Australian law degrees are not.
Therefore, doing postgraduate law at melbourne will be good if you are interested in working in the legal profession overseas.
As for an undergraduate degree, you can do anything that interests you. For someone interested in law, i would suggest arts, or possibly commerce. At the end of a bachelor degree you will be able to apply to be accepted into the postgraduate Juris Doctor, though be warned, you need a high pass rate for your undergraduate degree, and i would assume competition will be high, so be prepared to work hard in your undergraduate studies if you wish to get into law. Also, at melbourne, as part of the new Melbourne Model, you have to study breadth subjects from a faculty appart from the one which runs your degree (ie. i'm an arts student so i am doing economics from the commerce faculty). The key thing here is
the law faculty offers undergraduate breadth subjects which you can take when doing an undergraduate degree in arts, commerce, science, engineering and environments. Therefore, you will be able to take a few law subjects a year whilst doing undergraduate - so you won't be completely deprived of law for 3 years if you choose to study at melbourne!
Here are some useful websites if you haven't already been to them:
http://www.futurestudents.unimelb.edu.au/ugrad/ : this tells you what undergraduate degrees you can study at melbourne, and by following the links you can see the subjects available.
https://app.portal.unimelb.edu.au/CSCApplication/faces/htdocs/user/breadth/BreadthSearch.jsp you can get to this by following links from the first page, and it enables you to search specifically for breadth subjects so you can see what law subjects you could take doing an undergraduate degree.
http://jd.law.unimelb.edu.au/ this is the juris doctor webpage
Hope this helps
Ps. IT is possible for particularly high scoring school-leavers (99.9) to get a guaranteed pathway into Juris Doctor - ie. you can apply and if you do well enough in VCE/HSC they will offer you a place in the juris doctor - you will still have to do an undergraduate degree first, and maintain a relatively good grade average, but you won't have to compete for a place in the juris doctor later on. Check the JD website for details.
Also, you can apply for the juris doctor from any other university as well, so you can do undergraduate study at another university if you don't like the look/subjects at melbourne.