If you have a Google "Account" (the "sign in" link at the very top right of Google home page)...
... you can "install" into your account a whole host of extra google tools and services.
One of the most important is the Webmaster Dashboard, because it is here that you tell google where your XML sitemaps are, and invite them to come and index them. You also use this "dashboard" to keep track of what Google is doing with your XML sitemaps and you can react to any error reports google generates.
Google like this way of doing things because it likes the efficiency of it, and if you work closely with the SE's, providing such efficiency, your site gets a little more attention (because the SE's are following a MAP, not floundering in the dark)... So its very good for SEO.
Yahoo and MSN have similar features for webmasters.
The SE's use XMLSitemaps that must conform to the required convention (sitemaps.org), so this is where Andrew Berezin's XML-SITEMAPS comes into play... It generates the proper formats.