Dear Cat,
Perhaps you have already found the information you are looking for, but I figured I would update this thread even if only for others with the same question who may stumble across it.
In any event, eBay actually discontinued the "store item" format as part of a large set of pricing changes they implemented about a year ago. As of now, instead of having a separate listing format for eBay store subscribers, store subscribers just receive special discounts on the insertion fees for “fixed price” listings.
The cost of listing fixed price items through eBay for each level of eBay store subscriber are described on the following page of eBay's help index: http://pages.ebay.com/storefronts/Subscriptions.html
The items you post will show up in your eBay store whether you post them as “auction” of “fixed price” listings, but only items posted in the “fixed price” format qualify for insertion fee discounts related to your eBay store subscription.
I hope this helps. If you need any further assistance with your account, please feel free to contact our customer support team by mousing over the “Help” tab and selecting the “File Support Case” option.
-Mike