Just some more information on this:
Here's a little "quick start" tutorial describing how to use a sandbox bridge in an HTML-based AIR application:
Sandbox bridging sets up communication between the parent page (in the AIR application sadbox) and a child iframe or frame. To do this usingHTMLLoader.createRootWindow, load an HTML page from the application sandbox (an HTML file installed with your applicaiton) as the content of the created window. This page should use an iframe or frame to load the remote content, and it should define functions to be exposed via the sandbox bridge.
Thanks for the link Jeff - much appreciated. I see some of the dojo guys have packaged this up into an application here: http://www.sitepen.com/blog/2008/08/21/building-on-air-working-with-the-sandbox-bridges/.