Well, it depends on the subject, but it is generally the case at UniMelb that somewhere between 7%-12% of candidates in Arts subjects will be placed on an H1 for their final mark on the bell curve. Naturally, that makes it really competitive, especially because admission to Arts and Creative Arts courses at UniMelb is significantly higher than at NSW and other Victorian universities. But it's not unattainable, especially if you're motivated. I managed to get four H1s this semester.
I noticed that you've posted in a few of the forums and that you're looking to transfer into law. Unfortunately, next year will be the last year of undergraduate law at UniMelb, as the Uni implements its "Growing Esteem" strategy. You really should read more about that at the University's website -
http://www.unimelb.edu.au . Importantly, unless you gain admission into combined law at UniMelb through VTAC at the beginning of 2007,
you will not be able to take the course as an undergraduate student. Instead, you will need to complete your Arts degree and then study for a Masters of Law at the new graduate schools.
Good luck.