37372 Automatic product download

Hi I have a classified ads site that I want to make a change to. Most items that will be sold on the site will be normal items that are shipped which is fine thats how the site is set up however I want to be able to add a few downloadable items with buy it now button and once paid they can download the item straight away. I need it making so I can add downloadable items in the siteadmin area and these items display a Buy Now button, the customer then pays via PayPal and downloads the item. Only the site owner will be able to add these via siteadmin normal customers can't. I do need to be able to select category still though just like adding any item at the moment. This site is PHP so please only bid if you can edit PHP. If you have any questions please let me know Technical Retail