Hi Ronen,
The best MySQL JDBC driver is the one that MySQL publishes. You can find the latest stable/GA release here:
http://dev.mysql.com/downloads/connector/j/3.0.html
Also, storing XML in MySQL is easy! Just store it into a text or blob field. You can find more about these here:
http://dev.mysql.com/doc/mysql/en/BLOB.html
Also, if you want to explicitly store UTF8 XML documents and have MySQL handle this explicitly, then you can use the UTF8 character support in MySQL 4.1.
http://dev.mysql.com/doc/mysql/en/Charset-column.html
http://dev.mysql.com/doc/mysql/en/Charset-Unicode.html
Finally, I am not personally aware of any current OC4J migration projects, but can recommend that you look at Resin for a java web application server at
http://www.caucho.com/ for a very fast & stable web environment, and many of our clients have had success with them.
Regards,
Josh
Josh Chamas
Director, Professional Services
MySQL Inc., www.mysql.com
Get More with MySQL!
http://www.mysql.com/consulting