creation of sitemap.xml, learning each tag, each tag has own usages... I have using automated sitemap for creation..i'm using http://www.xml-sitemaps.com/ for creation sitemap.xml.....
XML Sitemaps are the best ways to tell search engine that these are the valid urls exist in website. and the priority level can be set for the google next crawl rate. so one can use it efficient way with respect to seo
I've always created sitemaps manually - most sitemap generators are garbage - bad metadata See here for more info on XML Sitemaps: google.com/support/webmasters/bin/topic.py?topic=8476