as long as the parent window opens a php page, you just need to add the add to cart button to it and set it to redirct to the cart page after the item is added to the cart. nothing special will need to be done.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.