submit and update sitemap.xml to Google

http://www.google.com/support/webmasters/bin/answer.py?answer=34609

To resubmit your Sitemap using an HTTP request:

1. Issue your request to the following URL:

   www.google.com/webmasters/tools/ping?sitemap=sitemap_url

   For example, if your Sitemap is located at http://www.example.com/sitemap.gz, your URL will become:

   www.google.com/webmasters/tools/ping?sitemap=http://www.example.com/sitemap.gz

2. URL encode everything after the /ping?sitemap=:

   www.google.com/webmasters/tools/ping?sitemap=http%3A%2F%2Fwww.yoursite.com%2Fsitemap.gz

3. Issue the HTTP request using wget, curl, or another mechanism of your choosing.