What this contribution is/does:
1. It's written for sites that use Separate Pricing Per Customer (SPPC).
2. It displays product listings in three columns (or 2, or 4, however many you want) instead of one long tall column as the stock osC product_listing.php does.
3. It gives the option of adding many different items to the cart at once, by having a quantity box underneath each item. Just enter in the quantity you want and hit the add to cart button!
4. It's really easy to install- just one new file and a few quick edits and you're off!