I'd disagree with Hknewbi's advice as I bought a Benq laptop from here Sept 2004 from mongkok and flew back to London pretty much the day after buying it, Unfortunately the HD failed but I had no problems at all in getting it repaired in U.K under warranty.
As long as the company has a presence and service centre back in Oz then you should have no problems at all, Stick to the tried and trusted brands such as Acer, Asus, Toshiba, Sony, Samsung and you'll be fine.
Broadway and Fortress have limited stock and they aren't at all competitive, some stores may only have a choice of 10 or so laptops whereas say wanchai computer centre you have a much wider choice.
Also with broadway/fortress you won't be able to negotiate on price, they might throw in something like extra ram but you'll have to go somewhere else to pick it up and install it yourself, too much hassle and expecially if you're only there for a week. Buy the laptop in your first few days as if you were very unlucky enough to encounter a problem with it you'll still have time to get it resolved.