Microsoft Live Search is finally now supporting sitemaps via autodiscovery. Microsoft will only use your sitemaps file if it is listed in your robots.txt file. You cannot currently ping Microsoft or upload your sitemaps file to Microsoft.
How do you specify the location of your Sitemaps file in your robots.txt file? Just add a line like this:
Replace the <sitemap_location> with the absolute URL for the file.
Microsoft, Search, Window Live, Live Search, Sitemap, Autodiscovery, Robots.txt