Adjusting PayPal plagin

I'm using Joomla v1.5.22 stable and e-shop Virtue Mart 2.0.8c. I need sale in my e-shop the art souvenirs which also sales in normal shop. [login to view URL] problem is that I can't control availability of goods in general. I think the solution is to get order without paying (status Pending) from buyers and check if that product is exist in normal store. If Yes than (status Confirmed) by admin and send email with link of checkout page to buyer to finish purchase. Otherwise send email that product out of stock. Editing by admin the order, if there is no some product delete it from order, after confirm order, send email with link of purchase and explanation of the order(what we have and not). I tried configure PayPal payment modul, but every time it's transact to payment gateway. Thank's in advance. And sorry about my English.