Dan, haven't you ever heard of XDoclet? Try adding a tag like this to your bean:
* @jboss.persistence datasource = "MySqlDS"
That should take care of your problem.
Dan, thanks for the suggestion. That sounded like a good idea. But after adding that tag my CMP entity bean is still using the Hypersonic data source. The MySQL datasource is OK - I can look it up and use it via JNDI, but I cannot get my CMP bean to use the MySql datasource instead of the Hypersonic one. Any further suggestions?