Wal-Mart's plans for a "Sustainability Index," a rating system that will assess its suppliers on their energy efficiency, responsible use of natural resources, and good practices regarding "people and community," made news back in July.The optimists argued the index could force a bunch of really big companies like Proctor and Gamble to get better about sustainability because they'd want to get positive ratings and stay in the good graces of the world's biggest retailer. There are also some complaints and caveats, of course.But as evidence that companies are taking the index seriously, side businesses are already getting set up to help them comply. This GreenBiz.com event is billing itself as essential preparation for corporate suits who want to understand the index's legal, environmental, and business implications. From the event description:The Sustainability Index is set to have a far-reaching impact in the management of supply chains. Whether you're a Walmart supplier, or a professional involved in supply chain management and sustainability, you can't afford to miss this important event.The sustainability consulting firm EORM will be at the GreenBiz.com conference hawking their "Readiness-Self Assessment Tool"-developed solely to help companies shape up for the Wal-Mart index.This is pretty clear evidence of Wal-Mart's ability to get companies to change. If the index also actually measures something meaningful-and it looks like it will (pdf)-its impact will be hugely positive.