ConnectionPooling 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
anew datasource implemented by org.postgresql.jdbc3.Jdbc3PoolingDataSource and with the serverName
dataBaseName,user,maxConnectionsand password properties set), I launch the server and during the execution I get an
exceptionwhich 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
notupgraded. 
I'm currently forced to use the Jdbc3SimpleDataSource class (with this class the application runs perfectly) but I
wouldlike to use Connection Pools to improve the application's performances. 

Thanks for having read my mail until the end :)