If you ever want to have the low order fee module on just one category, here is a code snippet to pull it off.

Edit file includes/modules/order_total/ot_loworderfee.php around line 62:

Code:
            // check to see if everything is gift voucher, if so - skip the low order fee.
              $charge_it = 'false';
              if ((($cart_content_type == 'virtual') and MODULE_ORDER_TOTAL_LOWORDERFEE_VIRTUAL == 'false')) {
                $charge_it = 'true';
              }
            }
          }

// Code to restrict to category

    $charge_it = 'false';
    $products = $_SESSION['cart']->get_products();
    for($i = 0;$i<sizeof($products);$i++) {
      $prod_cPath = zen_get_product_path((int)$products[$i]['id']);
      $pieces = explode('_', $prod_cPath);
      // 1960 is supplies
      if(in_array('1960',$pieces)) $charge_it = 'true';
    }
Just put in that piece of code and replace 1960 with your category ID.

I tried to install a drop down menu in the module to make this code a little more usable, but I didn't quite get there.