I suppost the issue is
Created directory : C:\ServerEnvironment\jbossas7\jboss-as-7.1.1.Final\modules\com\postgresql\main
Placed jar for driver and module.xml
<module xmlns="urn:jboss:module:1.1" name="org.postgresql"><resources>
if you look to the directory it is modules/com/postgresql and the module name org.postgresql.
Both should be the same!