I can give you a bit of an outline of my early entry experience if that would help (I hope I'm not too late, sorry if I am, as I only just noticed the thread).
What is the early entry interview like?
I had applied for two interviews, as there were two courses I applied for early entry for (Both within the informatics faculty, one being the BICT and the other for BIST). While there were some differences between the interviews, generally they were both very friendly, and relatively casual. We discussed my trial results, what had attracted me to the university, what my reasons were for being interested in the course, how I thought I would cope with the transition to University and that sort of thing. There weren't really any surprise questions in there, as long as you go to the interview with a solid understanding of why you're interested in the course, the uni, or even tertiary education, then I don't see this as posing too much of a problem.
what did you take down with you?
From memory (sorry, it was well, I guess around two years ago, maybe a little longer), I had already submitted a basic resume along with my trial results. I took a complete copy of my resume with me, including pretty much everything I could gather which I thought may be of use. Certificates, school reports, and stuff like additional qualifications (I had an OHS construction safety certification which I left in the folder, which strangely enough seemed to interest them and prompted quite a bit of conversation). I also took an additional copy of my trial results in case that was required. From memory, your UAC number is also a good idea, I forgot mine and had to fax it to them upon returning home (Perhaps all uni application related material could be stored in the back of your folder just in case it's needed)
Basically just include everything you can think of, if it doesn't interest them they'll flick past it and ignore it, which is far better than being unable to show them something which they are interested in, that you happen to have left at home (thinking it wasn't relevant)
Aside from my resume, I didn't take anything else with me.
What did you wear?
This was quite funny on the day, the majority of people wore tidy, semi-formal clothes. There were a few individuals who turned up in suits for their interviews, who (to me at least), seemed to look even more uncomfortable than required throughout the process. At the other end of the spectrum there were a number of people who turned up and looked well, less than presentable. That said, many of these people are now in my course, so I guess it must have worked out for them
In summary, what you wear probably doesn't make a huge difference, but if I had to make a recommendation I'd say tidy, not formal, but not overly casual
Personally I just wore a pair of pants (there's a surprise) with a short-sleeved collared shirt (being quite hot weather, long sleeves were out of the question, for me at least).
I don’t think I will reach the 80 UAI needed for the course, so im really relying on getting early entry.
You never know, you may be pleasantly surprised
I guess you probably already know, but even if you aren't granted guaranteed entry to the University as a result of your early entry interviews, they may set conditions which you need to meet in order to get in (Rather than making the UAI grade). Some of the people I've spoken to had conditions such as getting passes in Maths, or getting above a certain score for English, etc. They seem very willing to be flexible and allow you an opportunity to get in, even if you don't get the UAI they're looking for.
If you get it do they tell you straight away or what??
One of my interviewers said that he could see no reason that they wouldn't offer me a guaranteed entry, but that I'd have to wait for a letter to confirm it. The other interviewers (one was conducted by one person, the other by two) were much less forward and told me I'd get a letter in the mail. I forget the timeframe, but it seemed like a fairly long wait (Of course I was nervous as anything though, so that may account for it). My letter arrived one week before the commencement of the HSC exams, stating the outcomes of the interviews and letting me know where I stood with that.
There we go, I hope I've covered everything
If there's anything I've missed, or any more questions you'd like to ask just say so and I'll answer if I can. Good luck with the interviews, and with the HSC