Well.. Do you have:
SiteMap.ss in your templates/Layout directory? It should contain the code listed in the Tutorial (not an empty file).
You don't need to put $SiteMap in Page.ss as long as you use the Layout file (must have $Layout in your Page.ss)
You should have a SiteMap.php file in your code directory.
DB must be rebuilt.
In the CMS you'll have to create a new Page with type "SiteMap"
Maybe you should read through the tutorial once more and check if you missed something?