I've just finished my 3rd year at griffith, Nathan campus (I was trying to find this page for a friend in grade 12 and wandered into the forums). O week is ok, there's always a big party on one of the campuses, this year it's back at Nathan. If you're underage it's not as fun, but if you're 18 it's fine.
There's a lot of freebies floating around, make sure you scab as much as you can from the market stalls...
If you want more info ask away...accommodation may be hard to find this late, though there are a lot of student complexes around that are great to live in (I've been in one the past 3 years, am hopefully moving out soon). Don't go on campus if you're at Nathan, unless you really want the on campus thing. It's much easier to live in one of the complexes scattered around (Uni Park, Griffith Glen etc), and much nicer.
The timetabling and enrolling thing is a bit tougher this semester, because we used to not have online sign ups for tutorials, but they've added that to all courses this year so you have to plan your timetable before you enrol which is a pain.
Oh and check the second hand bookshop before buying your textbooks, and the posters around uni as well, unless you're doing a biology course (and Im sure there are others that are hard to find books for), there are lots of people selling second hand ones. If you need to get 'Chemistry' by Brown, then make sure you go to the bookstore (above the food store, in the SRC room), because there's always copies of that available.