Here is a stick figure picture of atlatl being used.
http://www.thunderbirdatlatl.com/articles/tour/tour3.html
http://www.ohiohistorycentral.org/ohc/archaeol/p_indian/pictures/atlatl.shtml
Here is a very long but authoritative article about whole atlatl problem.
http://www.atlatl.net/article.asp?articleid=1