Several project members regularly hang out on the 2 IRC channels dedictaed to Hibernate-related discussions:

• irc.freenode.net/#hibernate - Is a user-focused channel intended for discussions of Hibernate usage.  This is a great place to start with questions.
• irc.freenode.net/#hibernate-dev - Is a channel where Hibernate developers and contributors discuss development of Hibernate. In oder to join #hibernate-dev you will have to register your nickname. Just follow the instructions here.