Not finding the table and opening a database

I'm trying to write a standalone program that uses EJB persistence and I 
have two problems:

1) How can you set up the connection so that it will open the database 
if it exists and create one if it doesn't?

2) When I try to persist an object, it tells me that the table doesn't 
exist.  I'm using hibernate and mckoi and I was under the impression 
that the persistence layer would take care of creating the table.  What 
could I be doing wrong?

Here's my error listing:
Exception in thread "main" javax.persistence.PersistenceException: 
org.hibernate.exception.GenericJDBCException: could not insert: [Item]
    at 
org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:630)
    at 
org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:219)
    at DatabaseClient.main(DatabaseClient.java:60)
Caused by: org.hibernate.exception.GenericJDBCException: could not 
insert: [Item]
    at 
org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:103)
    at 
org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:91)
    at 
org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
    at 
org.hibernate.id.insert.AbstractSelectingDelegate.performInsert(AbstractSelectingDelegate.java:40)
    at