You can do so through various online services. For example; http://www.xml-sitemaps.com/ If your using wordpress, you can use the google xml sitemap plugin; http://wordpress.org/extend/plugins/google-sitemap-generator/ If you want to create your own, then it is not overly complicated; you will need to obviously select your posts/articles/etc from your database and perocess them according to the spec; http://www.sitemaps.org/protocol.php
hey mate in another thread sm 1 asked the same question and sm 1 gave a great answer ie to download the software called sitemapwriter its trial is availible and u can also google a cracked version this is really good the site is http://www.sitemapwriter.com/
Thanks for that dude, I just got one too, and it works just fine, especially happy with such fast crawler.