I was getting the same problem you describe.
The error is very cryptic. Surprising given the wide acceptance of Hibernate that it would have some sort of static method on Configuration to give you the configuration and a meaningful exception if the dependencies for a Configuration cannot be loaded or accessed.
Also helpful would be a clear identification in the manifest of the required apis and versions for the implementation of hibernate you are using.
Was scratching my head as I new the jdbc driver I was looking for was in my classpath as was hibernate3.jar the commons jars, and some of the others.
It is not the jars you identify. You need some additional dependencies for hibernate in your class path.
Try adding the following jars that are listed in the reference document:
Hibernate Reference Documentation vs: 3.2.2 on page 10.
antlr.jar
cglib.jar
asm.jar
asm-attr.jar
commons-collections.jar
commons-logging.jar
hibernate3.jar
jta.jar
dom4j.jar
log4j.jar
I searched the hibernate site and found
http://www.hibernate.org/27.html
and the section * Projects Used By Hibernate. With links to the mentioned resources.