If I put Hibernate Validator 3.x to the classpath, hibernate-core used it automatically.
Now I tried putting Validator 4 to my classpath, but hibernate-core ignored it.

How to integrate Validator 4 into hibernate-core??

Which hibernate-core version is the minimum required?
Had I to use Hibernate Entitymanager or does it work without Entitymanager?
Is JPA2 required or JPA1?

You need Hibernate 3.5, but that's so far only in a beta state.
You might find this thread helpful. I shows how you can use Hibernate Validator 4 with an older version of Hibernate Core - viewtopic.php?f=9&t=996940

--Hardy