Sounds great congrats!!! I tried but I was unsuccessful. I have the latest zen cart and lightbox 1.4. I currently have my attribute images setup this way. I go to attribute controller and add a picture at the bottom. The images are in images/attributes/
This is to have the images change which works on all the products except for one actually. I followed your post and read over it again and again to make sure. Here is what my portion of attributes.php looks like.

Code:
     if ($products_options->fields['attributes_image'] != '') {
                      $tmp_attributes_image_row++;

                      //              if ($tmp_attributes_image_row > PRODUCTS_IMAGES_ATTRIBUTES_PER_ROW) {
                      if ($tmp_attributes_image_row > $products_options_names->fields['products_options_images_per_row']) {
                        $tmp_attributes_image .= '<br class="clearBoth" />' . "\n";
                        $tmp_attributes_image_row = 1;
                      }
					  
					  
					  
					  
					  
					  
					  
					  //find large size attribute images. Location must be in /images/large and image name must be image_LRG.ext Mike Scott 070606				
					$array_filename = split("[/\\.]", $products_options->fields['attributes_image']) ;
					$filename = $array_filename[count($array_filename)-2];
					$extension = '.'.$array_filename[count($array_filename)-1];
					$filename = $filename.'_LRG';
					$path = DIR_WS_IMAGES . 'large/attributes/';
					$attribute_image_lrg = $path . $filename. $extension;
					$selected_attrname = $products_options_names->fields['products_options_name'] . ': '.$products_options->fields['products_options_values_name'];
					  
					  
					  
					  
					  
					  
$tmp_attributes_image .= '<div class="attribImg"><a href="' . $attribute_image_lrg . '" rel="lightbox[gallery]">' . zen_image(DIR_WS_IMAGES . $products_options->fields['attributes_image']) . (PRODUCT_IMAGES_ATTRIBUTES_NAMES == '1' ? '<br />' . $products_options->fields['products_options_values_name'] : '') . '</a></div>' . "\n";
                    }
                  }

I then added a picture into the images/large/attributes folder with the image_LRG.jpg format. I see now difference. I am hoping I am missing something because I would really love for this to work.

Can I see a link to your site. Do you have any ideas what I could have done wrong?