Hm, depends on what the grading system is like, and assuming that its the same as NSW unis - but I personally found that first year was harder than second year, in terms of doing well for arts. I'm about a low 80-something for Arts atm, but theres a certain writing style required in Arts that is quite different to High school, so I found it difficult to get Ds initially. However, this depends on the person and how hard you work. My general rule of thumb is that its easy to pass Arts but more difficult to get up to the High Distinction range, particularly as its so subjective. But if you work hard, a high credit/distinction average wouldn't be too hard, and if you manage to get a hang of the Arts style, a distinction average (even HD) would be definitely attainable.
Hope that helps!