It's not that easy, the JBoss Cache provider is hardcoded last time I checked. This website (/examples/wiki) uses EHCache though and you can look at the code to see how that was done.
Be aware that it's also using the same EHCache instance (with different regions) for Hibernate second-level data caching and HTML page fragment caching. That particular setup depends on the deployment order of persistence unit and Seam, which changed in JBoss 5.x. In other words: If you want to also use EHCache for both and copy the setup 1:1 from the example code, use JBoss 4.2.x.
Oh, and it looks like what you are trying to do in your code example is not a good idea and you probably don't know much about data caching in Hibernate. Read up on that first before you do anything else.
I add the <cache:eh-cache-provider> in components.xml, and put ehcache.jar into lib dir, the it works