You should have two sitemaps on your website, one that is for your human visitors to look at and one for the search engine bots to check over, there jobs are different as is their layout the site map for people is normally created in HTML and the sitemap for the search engines would need to be an xml sitemap.

The human html site map should be simple to follow, it is used by visitors to your site in case they can not follow the logic of your links to find the page they are after it allows the user to go into one place and look at the page names and titles to establish how to find what he is looking for.

Xml is a format that was agreed by the big 3 search engines, Google, MSN and Yahoo to allow webmasters to create just one site map for the search engines that they could all follow rather than requiring 3 different formats to do the same job.

The xml sitemap is designed so that the search engine bots can look at it and find the links to all the pages you need them too, you are able to set different parameters such as the regularity of the updates of the pages, so you can tell the bots how often a page is updated and how important it is to your site.