I worked at a circuit city store once before (very briefly!)... here are snippets of what I was asked/told to do during the very informal/spontaneous interview that I had (though it was a brutal 1 hour long!)
-What gadgets do you own?
-Describe how you would make a sale.
-How have you made sales in the past?
-How would you approach a customer entering the store?
-Why are you quitting your current job?
Most of the questions pertained to sales, though. Once I started, I realized that I knew a lot more than a lot of my coworkers re: electronics (which isn't even all that much!)
I think the best advice I can give, though, is just to sell yourself really well, and make a good closing statement as to why you should be hired (the person hiring had me make one up on the spot.)
I have never been to Harvey Norman, but I am assuming that it is the same as any other electronics store, in that they are most concerned with the bottom line. Therefore, you must show that you are sales savvy as well as knowing something about the products that they are selling.
