Best bet is to have a look here:
http://www.ms.unimelb.edu.au/~mums/puzzlehunt/ and review the previous years' hunts.
CiSRA is going to be a bit later this year, at the end of April or beginning of May apparently - see
http://puzzle.cisra.com.au/ for a bit more info.
You may have heard of the MIT Hunt, sometimes mentioned by Scurra and myself (the 2009 MIT event was held in January). It's along those lines, although MUMS and CiSRA hunts are generally somewhat less intense - tending to be a timed release of puzzles over 5 days rather than about 100 - 150 puzzles over a single weekend, so don't be frightened off by thoughts of it being quite like MIT as described.
CiSRA is open to
teams of four registered people, but allowed to have unlimited "unofficial helpers" - the official restriction is only for legal reasons because it's a commercial organisation offering a prize, but as only Australian students are eligible to win any prizes, it's pretty irrelevant to PBers.