JDBC Transaction Isolation level 4 - Serializable problem

I can't seem to get the JDBC driver to accept serializable transaction
isolation levels.

Does the driver support it ?

I have tried with pg73jdbc1.jar, pg73jdbc2.jar, pg73jdbc2ee.jar,
pg73jdbc3.jar and devpgjdbc3.jar.

The error that I am getting is :

org.postgresql.util.PSQLException: Transaction isolation level 4 is not
supported.
    at
org.postgresql.jdbc1.AbstractJdbc1Connection.setTransactionIsolation(AbstractJdbc1Connection.java:1414)

If this is the case (that it's not supported) are there plans to
implement it ?

I can't fund any specific information on the driver's features on the
internet.  Either at jdbc.postgresql.org or through google.

Thanks,

Cameron

--
Any damn fool can write code that a computer can understand...
The trick is to write code that humans can understand.
[Martin Fowler http://www.martinfowler.com/distributedComputing/refactoring.pdf]