I'll take a swing at this.
Hibernate is an Object Relational framework. It is owned by JBoss. It can be used in Java Enterprise Applications, as well as in Java SE apps. It works using POJO's and a descriptor, and I think it now supports annotations, so you don't need to do the descriptor.
JPA is a specification for persistance of POJO's. JPA makes heavy use of annotations, but it can also use an XML descriptor. JPA is not an implementation and each vendor must provide one to be JEE 5 compliant.
JBoss has a JPA implementation that uses Hibernate under the hood. If you use JPA on JBoss you will not use Hibernate specific syntax to do your work. You would use the JPA standard stuff. JBoss will make it all work behind the scenes.
Thanks, it helps