Java auction - where do i start?

I have recently been given a uni project which involves programming an auction as a java applet. Im really looking for pointers and/or things i should look out for during the making.
Also, i need to make a system whereby i can automatically increase or decrease the number of items in the auction system... ideally i would have a multi-demensional vector but since they dont exist, i have to somehow manage with a multi-dimensional array. Any tips would be much appreciated... URLs to tutorials or other useful references would be even more appreciated.
Please dont point me to the javadocs, i already know where they are

thanks.

You could use a vector of vector of vector... if you want to. You could even create your own collection class called MDVector or something like that.
Here is a digest that proposes some "solutions":
Topioc of the day: multidimensional Vector?