If you want to make a proper sitemap that gets automatically updated please use http://www.google.com/support/webmasters/bin/answer.py?hl=en&answer=156184&from=40318&rd=1 as your starting point.
Google offers the possibility to automatically create a sitemap and update this based on the page visits. You will have to read the instructies carefully.
If this is not what you are looking for you might wat to consider creating a XML sitemap using an online tool, such as: xml-sitemaps.com
The idea of a sitemap is to have this point to all pages. You can, however point out the importance of each page using the priority tag.
Please note that a XML sitemap is for you to submit to the search engines and and HTML sitemap is to be viewed by your website visitors. Its recommended to have not more than 100 links per page.