For building Play 2.0 I followed this recipe (beware - bleeding edge ;-)
$ git clone git://github.com/playframework/Play20.git
$ cd Play20/framework
$ ./build publish-local
$ PATH=$PATH:Play20
In an Eclipse Workspace:
$ play new test20
$ cd test20
$ play eclipsify
$ play ~run
In Eclipse:
- Preferences/General/Workspace: Enable "Refresh using native hooks or polling"
- File/Import.../General/Existing projects into workspace...