But Wait! There's More!
Google isn't the only site that uses Sitemaps. Yahoo! Search does, too. You can follow a similar process to tell Yahoo! about your sitemap. Start by following the instructions that appear online to create a Yahoo! account, log in, identify and verify your Web site, and tell Yahoo! about your sitemap.
Evidently, MSN will be able to support sitemaps someday, but I was unable to find out how to submit one—and I looked pretty hard. So I think it's safe to say that your sitemap won't help you with MSN—at least not yet.