Its very easy quick & very useful, just :
1 - Copy and past the url (line) in your navigation barre
2 - Replace your-website.com by your real domain name
To ping Google
http://www.google.com/webmasters/sitemaps/ping?sitemap=http://www.your-website.com/sitemap.xml
To ping Bing
http://www.bing.com/webmaster/ping.aspx?siteMap=http://www.your-website.com/sitemap.xml
To ping Ask
http://submissions.ask.com/ping?sitemap=http%3A//www.your-website.com/sitemap.xml