Our format of our demos zip file for JDK7 was changed (see JDK-6608999). Unfortunately, this change means that the Readme file located in the jdk1.7.0_21/demo/nbproject/ directory is wrong (file attached).
Given that we are providing NetBeans project support files, it would make sense for this to work as documented in the readme file. The request is simply to expand the src.zip files, and for someone to test to ensure that the projects are successfully loaded in the latest NetBeans (at this time it is 7.3).