To install the datasource for MySql I have installed the jar in the folder "C:\jboss-as-7.1.0.Final\modules\com\mysql\main". Sure the directory is the same "C:\jboss-as-7.1.0.Final\modules\com"
I consulted this website: http://marceloagustini.wordpress.com/2011/09/23/agregar-mysql-datasource-jboss-7-x/
Fran