This is the website to check out if you want to learn more about Sitemaps: http://www.sitemaps.org/protocol.php
I usually do my sitemaps in PHP. So, I am going to break new ground here and drop some code on my blog. Since most of my sites are now PHP, here is what I typically use:
<?PHP header("Content-Type: text/xml; charset= UTF-8"); ?>
<?PHP echo "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"; ?>
echo date ("Y-m-d", filemtime("index.php"));
same stuff here...
... and add more urls as needed
Make sure you test the URL in your browser first, but then it should be good to go. You can let the search engines know about it in the webmaster tools or even add a reference to it in your robots.txt file ("Sitemap: http://www.mydomain.com/sitemap.php").