The Daintree website is an excellent resource for those embarking on a Zigbee project. They have whitepapers, tutorials, demos that help you understandthe basics of Zigbee networking (specifically their Zigbee primer whitepaper) and application profile object model in Zigbee.
http://daintree.net/partners/ti-chipcon.php
Their sniffer tool is a powerful ally when debugging Zigbee systems.
May the SNA be with you, always....