Alla fine ho realizzato cosi!
configurazione di hibernate:

<hibernate-configuration>
<session-factory >

<property name="connection.datasource">java:comp/env/jdbc/nomewebapp</property>
<property name="transaction.factory_class">org.hibernate.tra nsaction.JDBCTransactionFactory</property>
<property name="dialect">org.hibernate.dialect.MySQLDialect</property>
<property name="current_session_context_class">thread</property>
<property name="hibernate.show_sql">false</property>
<property name="hibernate.generate_statistics">false</property>

<property name="hibernate.cache.provider_class">org.hibernat e.cache.EhCacheProvider</property>


</session-factory>
</hibernate-configuration>

Ho creato sotto la directory META-INF della mia webapp, il file context.xml cosi composto:

<?xml version="1.0" encoding="UTF-8"?>
<Context
reloadable="true"
workDir="\work">
<Resource
name="jdbc/nomewebapp"
type="javax.sql.DataSource"
driverClassName="com.mysql.jdbc.Driver"
factory="org.apache.commons.dbcp.BasicDataSourceFa ctory"
password="password"
initialSize="3"
maxIdle="10"
minIdle="5"
maxWait="10000"
maxActive="10"
username="root"
url="jdbc:mysql://nomeserverorta/nomewebapp"
removeAbandoned="true"
removeAbandonedTimeout="60"
/>
</Context>

Funziona tutto correttamente ma ho escluso il discorso jndi che rimane un po' oscuro...
Se qualcuno puo' darmi lucidazioni....
Grazie