Offline "Updater"

Hi again guys - this is getting a regular habit, but all is expanding my somewhat limited knowledge!

Basically, I wanted to know do you know of any ways (or indeed any software programs) to create a piece of software which you can store data in for a shopping app like osCommerce and then once you've added all the data, with pictures etc, you can upload it and it adds the products onto the website. A pain I know...but the guys I am doing this for don't have Broadband/Cable and cannot get it because they're too far away from the Exchange. So basically, they want to limit their time on the net (otherwise I'd have used osCommerce's online Admin!). They also want to use this updater both at Home and at their shop so it needs to be interacting with the other as well...

They cited the example of TurboLister off eBay. Mainly because up until now they've been selling their stuff off eBay and now wish to get a website...I kind of get the impression that whatever I come up with, whether made myself or researched on the internet, will be compared to this so I guess it needs to be quite good "from the front".

The type of things they will need to modify/add/delete are :

Product Names,
Prices,
They want to edit images,
Product Descriptions,
and various other bits and pieces if necessary.

So...how easy/hard will it be to create something like this? I presume it would be incredibly difficult...but you never know!