For general database configuration (to access the database from your application), see http://docs.jboss.org/jbossas/guides/j2eeguide/r2/en/html/ch7.chapt.html#ch7.jdbc.sect (Configuring JDBC Datasources)
To replace Hypersonic (and thus DefaultDS) with your database, see http://wiki.jboss.org/wiki/Wiki.jsp?page=SetUpMysqlAsDefaultDS
Not yet finish. please tell me more detailt. I can't see any file like this guide. :(.
From the document link that I posted:
Example configurations for many third-party JDBC drivers are included in the JBOSS_DIST/docs/examples/jca directory. Current example configurations include:
Edit that file to contain your database connection information, and then copy it to server/default/deploy.