okay, more questions 
1) humph/eriny or both, do you guys remember what your first day at ANU was like? if you do, was it easy to just mix in with people and stuff?
Can't remember much of O-week in my first year, oddly enough (and I was sober most of the time too! Well, more sober than I was for O-week in second year...). None of the first years at college really know each other on the first day so there's lots of meeting new people, trying to remember everyone's names, working out where everyone's from, working out who has similar interests to you, is doing the same course as you, if you have any mutual friends etc (e.g. the sister of one of my friends from college went out with my cousin. Bizarre). The later years at college try to help the first years mingle a lot and have events that encourage socialising and so on.
Obviously a lot of people are really shy at first (and who could blame them, most have moved a fair way away from home and don't know anyone) but the colleges try to make it easier for you to move out of your comfort zone and meet new people.
It's surprising, but after three or four weeks or so, all of a sudden you realise you have these really good friends.
2) do you come back to melbourne at any time other than the summer holidays? can you stay at ANU during other breaks if you want to?
thank yo
At most colleges, the room contract is for 40 weeks; pretty much from Feb 15 to Nov 24 or so. Or something like that. Anyway, you can definitely stay at ANU during the other breaks. The spring and autumn breaks are usually two weeks and plenty of people stay during this time. The winter break is 4-5 weeks or so and you'll find that it can get extremely empty at college during these holidays - this is normally when everyone goes home for a week or two.
I've been known to just fly down for a weekend in the middle of term in order to catch up with family and friends. If you organise your timetable right you might even have a couple of days off uni every week, which makes it easier to go home for a long weekend or something.