The CMS uses jackrabbit. You will find the lucene index is disabled by default in 2.4.
In 2.2, you will find it under jboss-x.x.x/server/default/data/portal/cms/conf/workspaces/index/ i believe.
This article talks a little about how to use the jackrabbit api to search: http://www.artima.com/lejava/articles/contentrepository.html
Keep in mind the index creationg mechanism is disabled in 2.4, as we have to account for clustering support.
That is what I wanted, the only problem is that I have no idea about how to get the the "session" from a Tapestry aplication in order to call the following line.
(Workspace ws = session.getWorkspace();)
I'm new to all this framework, Can you give me a hand?