I’m posting this as a note to myself because I keep forgetting how to do it between drops of the AIR 2.0 Beta SDK.
This article tells you everything you need to know. The key for me was the helpful “ditto” command:
[code lang="as3"]ditto -V /Volumes/AIR\ SDK/ /Applications/Adobe\ Flex\ Builder\ 3/sdks/3.4andAir2/[/code]
You can apparently also use “cp -r”.