Well, if you're using the AIR Install Badge - as Greg Wilson demonstrates - it can be surprisingly easy. The Install Badge handles the launching of your application (if you have it already installed), the installation of your application (if you have the AIR framework installed), and the installation of the AIR framework and the subsiquent installation of your application if you have neither.
The whole Flash / AIR auto-updater can be a pain to sort out when you do it yourself, but the result is very efficent from the end-users' perspective. Lucky then that the Install Badge template has this sorted for you.
When the 'AIR framework requirement' is a hurdle for getting clients to adopt an AIR solution, the ability to auto-install the AIR framework is a powerful arguement...
See Greg Wilson's post here: http://gregorywilson.wordpress.com/2008/08/21/air-install-badge-use-it/