how to add jpa entity in ejb project from eclipse juno?

i am following ActionBazaar example from manning ejb3 in action book. uptil now i have created an enterprise application project in eclipse and added web modules and ejb modules . in ejb module i have created session beans and message beans. now i would like to add an jpa entity in it. when i did new > create new jpa entity , the dialog box won't allow me to do anything. at the top it says that "only jpa enabled projects may be selected ". in the projects dropdown no project is coming, so i'm unable to proceed. please help?