The Google Sitemap Protocol allows a webmaster to inform search engines about URLs on a website that are available for crawling. A Sitemap is an XML file that lists the URLs for a site. It enables webmasters to include additional information about each URL: when it was last updated, how often it changes, and how important it is in relation to other URLs in the site. This allows search engines to crawl the site more intelligently. Sitemaps are particularly beneficial in situations when it is difficult for users to access all areas of a website through the browseable interface. For example, a site with a large "archive" or "database" of resources that aren't well linked to each other (if at all), only accessible via a search form. The webmaster can generate a sitemap containing all accessible URLs on the site and submit it to search engines. Note that the Sitemap Protocol is only a supplement and does not in any way replace the existing crawl-based mechanisms that search engines already use to discover URLs. By submitting a sitemap (or Sitemaps) to a search engine a webmaster is only helping that engine's crawlers to do a better job of crawling their site(s).

There are a number of applications on the web that will accomplish this task. They will either crash your PC and or will take multiple days to complete. This modification will create the entire feed in just a matter of seconds.

Installation is extremely simple.

Requirements:

1) Know how to run a SQL query on your DB for the install.
2) Know how to setup a cron from your host control panel.
3) Have the ability to setup a free account with google and with yahoo.

Once operational, Google will come for your sitemap 1 time per day.
Once operational, Yahoo will come for your sitemap, but you will need to manually request it.
(Yahoo does not yet offer an automated retrieval of the file).