PoolingDataSource executeUpdate

Hi everybody!
First excuse me for my poor english, I'm not a native english speaker :-).

I have problems with the ConnectionPooling Implementation of the 4.3 postgresql
jdbc driver: (pg74.214.jdbc3.jar).
I'm using the 4.3-1 postgresql server under windows 2000 with cygwin.
There is my problem:
I am trying to comunicate with this datasource from a web application(the web-
server is websphere 5.1 and we use jsp,servlets...).

First I cannot manage to configure the datasource so that the application takes
it in account (with WSAD5.1 I configure a new datasource implemented by
org.postgresql.jdbc3.Jdbc3PoolingDataSource and with the serverName
dataBaseName,user,maxConnections and password properties set), I launch the
server and during the execution I get an exception which says something like
Driver cast exception this driver cannot be used as one phase.

So I tried another thing, instead of configuring the datasource with the
websephere interface I configure it with javacode (I know that I may not do
that because the code results to be less portable). So there is my code:

Jdbc3PoolingDataSource pgSource = new Jdbc3PoolingDataSource();
pgSource.setServerName("localhost");
pgSource.setDatabaseName(dbName);
pgSource.setUser(userName);
pgSource.setPassword(password);
pgSource.setMaxConnections(numberOfMaxConnections);
ds = (javax.sql.DataSource)pgSource;

and to obtain a connection I do:

Connection con = ds.getConnection.

I launch the server and test it. All the select queries work well, but when I
try to do the first update of the database:

query = new StringBuffer();
query.append("UPDATE ");
query.append(ServiceTable);
query.append(" SET ");
query.append(ServiceDescDocId);
query.append(" = ?, ");
query.append(ServiceHelpDocId);
query.append(" = ? WHERE ");
query.append(ServiceId);
query.append(" = ?");
// Execute the query:
psmt = con.prepareStatement(query.toString());
psmt.setString(1, ddId);
psmt.setString(2, hdId);
psmt.setString(3, svcId);
numUpdates = psmt.executeUpdate();

What happens there is that with Connection Pooling the executeUpdate method
always returns 0, and that the database is not upgraded.
I'm currently forced to use the Jdbc3SimpleDataSource class (with this class
the application runs perfectly) but I would like to use Connection Pools to
improve the application's performances.

Thanks for having read my mail until the end :)