Custom Online ecommerce with store based inventory integration

I require an ecommerce/shooping cart system as an addition to our store website http://meleegaming.com. This addition would have to be similar in execution to [login to view URL] Adding product needs to be easy and efficient. I already control the domain meeleegaming and sufficient webspace. I control one mysql database, but do not own a ssl or credit processing suitable for the internet. Here is the catch. I want the inventory in the store to be synched with the online database. This would prevent me from having two separate inventories. This way when someone attempts to purchase an item in the store that was already purchased online the inventory will show me 0 in stock. Our inventory is done through a program called cash register express, a pc based register system. The trial can be downloaded here: [login to view URL] I have looked through the system files and don't see where the inventory is saved, but there are some mysql databases, which would make things easier if they are stored that way.