I think you'll have to download the SDK and st it up yourself; but Flash Builder should work fine:
http://labs.adobe.com/wiki/index.php/AIR_2:Release_Notes
How to overlay the Adobe AIR SDK for use with the Flex SDK
- Copy the contents an existing Flex SDK folder to a new folder. For
example, in Flex Builder, copy the
following folder located at:
* Windows: c:\Program Files\Adobe\Flex Builder 3\sdks\3.2.0
* Mac OS: /Applications/Adobe Flex Builder
3/sdks/3.2.0
- Download the appropriate AIR SDK file for your operating system and
save it to the root folder of the Flex
SDK.
* Windows: AIR20_win_sdk_XXXXXX.zip
* Mac OS: AIR20_mac_sdk_XXXXXX.tbz2
Extract the contents of the AIR SDK archive and overwrite the existing
SDK files in the copied folder.
* Windows: Right-click on the ZIP file and select "Extract All"
or use the decompression tool of your
choice.
* Mac OS: In Terminal, cd to the root folder of the Flex SDK and
run this command:
* tar jxvf AIR20_mac_sdk_XXXXXX.tbz2
If you have trouble overwriting files due to file
permissions, try this command
sudo tar jxvf AIR20_mac_sdk_XXXXXX.tbz2
In Flex or Flash Builder, open the Properties dialog and choose the
Flex Compiler page
- Click the Configure Flex SDKs... link
- Add the combined Flex and AIR 2 SDK folder created above
- Use this SDK for any projects accessing AIR 2 APIs.
To update this for the production release; go downlod your preferred version of the Flex SDK at http://opensource.adobe.com/wiki/display/flexsdk/Downloads and download the AIR 2 SDK at http://www.adobe.com/cfusion/entitlement/index.cfm?e=airsdk .
Overlay the two using the instructions above (1-3); then configure the new SDK in Flash Builder (also using the instructions above (4-7).
Update: Since my original post of this; Flex 4.1 SDK was released which includes the relevant AIR 2 bits. You can get it here