Download adobe flex 4.5.1 Sdk from here join Adobe Air 3 sdk downloaded from here.
Download Alternative 3d 8.12.0 SWC from here.

Create a Air project on Flex Builder 3, add “-swf-version=13 -static-link-runtime-shared-libraries=true” to additional compiler arguments on project properties . Add “<renderMode>gpu</renderMode>” below “<initialWindow>” on app.xml and you are ready to go. You can download here a simple example of a pac-man style game.

Note: to test your application install adobe air 3 & flash player 11