Hi jeric82,
The store window is set to display 12 items at a time favoring items that are ending around the same time as the item being viewed, and is refreshed every 4 hours. We will be increasing the store window capacity to 20 in the near future.
The only way you can control what goes in your store window is by making items featured/hidden.To do this, go to Auctiva -> Store(tab) -> Store -> Edit/Preview -> Featured Items. Items that are made hidden will not be shown in your store window and items that are featured will always be shown(as long as there aren't more than 12).
There's no way to make a new listing auto load into the store window but you could feature it and that would cause it to be displayed in your store window.
I hope that clears things up!
-Mike