This is an excellent new step in the world of SEO. Google, MSN and Yahoo! have teamed up to provide a uniform protocol for submission of sitemaps to all three search engines.
Webmasters who provide an XML Sitemap can now just include reference to it in their robots.txt file as follows:
Sitemap: http://www.sitename.com/sitemap.xml
The above line can be placed anywhere within the robotx.txt file, which is widely accepted as the standard robots access / exclusion protocol by all search engines and is typically the first file accessed by the search engine spider when it accesses any site.
The Live Search blog provides a detailed post at
Sitemaps auto-discovery by Google, Yahoo! and MSN Live Search