title: Magento dropdown with existing products
body: <p>I was wondering if it's possible in Magento to make an attribute with a dropdown input type in wich you can select existing products.</p>
  
  <p>If so how would one go about in doing this?</p>
  
  <p>Also if someone knows how to display the simple products inside a grouped product on the category(catalog) view, that would be real helpfull aswell.</p>