It's already been 4 years ago since I worked on the actionscript port...
There is a client application in Actionscript which works without having to compile anything.
The repository is :
https://github.com/rethinkbooks/zxing/tree/master/actionscript
Put it on a webserver and open the following html file in your browser.
http://<<your webserver url>>/zxing/actionscript/zxing client/bin-debug/zxing_client.html
If you don't have a webcam present you can just click OK and press the 'select image' button. Select an image from the zxing/core/test/data/blackbox.
Make sure you select the type of barcode you would like to decode on the bottom right of the application and press 'Decode!'.
If all goes well then the result will be displayed.
This sample application shows how to integrate all the funtionality in your own application.
It's been 4 years since I've worked on this stuff so a recent version of FlexBuilder might throw out some warnings.