See if you don't have any hb libraries in your classpath - either in tomcat common/lib, shared/lib or inside WEB-INF/lib. Start your application and make sure hibernate is not found.
After that get the official Hb3 from hibernate.org (or from Spring-w-deps) and place it in shared/lib. Hibernate has some dependecies - you can read them inside the readme.txt.
From there everything should go smooth.