Problem with Java-SQL connection, postgresql.conf file

Hallo,

I want to establish a connection to an SQL Database from a
Java Applet which is situated on the same server. I used the
interface postgresql-8.2dev-503.jdbc3.jar. I use
NetBeans IDE 5.0 (Sum Microsystems) for the development of
Java Code. I copied postgresql-8.2dev-503.jdbc3.jar into the
build/classes folder of the project containing the Applet
and made it accessible for Compile and Run as a Library of
the project
(Project -> Properties -> Libraries -> added
postgresql-8.2dev-503.jdbc3.jar to Run and Compile). I also
added postgresql-8.2dev-503.jdbc3.jar as a driver
(Runtime -> Databases -> Drivers -> Add Driver -> PostgreSQL
(v7.0 and later) is accessible).
Moreover I unpacked the jar file into the build/classes folder
and uploaded all files contained in the build folder to the
server (SERVER_SOFTWARE: Apache/2.0.54 (Fedora)).

I used essentially the following Java code (Java 1.5.0_07)...

////////////////////////////
import java.applet.Applet;
import java.sql.*;

public class O17 extends Applet implements Runnable {
private Thread worker;

public synchronized void start() {
if (worker == null) {
worker = new Thread(this);
worker.start();
}
}

public void run() {
String url = "jdbc:postgresql://localhost/<DB>";

try {
Class.forName("org.postgresql.Driver");
} catch(Exception ex) {
setError("Can't find Database driver class: " + ex);
return;
}

try {
Connection con = DriverManager.getConnection(url,
rightuser, rightpassword);
Statement stmt = con.createStatement();
stmt.executeUpdate(createTableCoffees);

stmt.close();
con.close();

} catch(SQLException ex) {
setError("SQLException: " + ex);
}
}
}
////////////////////////////

... and different variations of the url which produced the following error codes:

jdbc:postgresql://localhost:5432/<DB>
jdbc:postgresql://localhost/<DB>
jdbc:postgresql://<DB>
->org.postgresql.util.PSQLException: Etwas Ungewöhnliches ist passiert,
das den Treiber fehlschlagen liess. Bitte teilen Sie diesen Fehler mit.

jdbc:postgresql://molekuelkueche.de/usr_web593_1
->org.postgresql.util.PSQLException: Der Verbindungsversuch schlug fehl.
(SERVER_NAME = www.molekuelkueche.de)

Moreover I searched for the postgresql.conf file but I could not find it
among the files extracted from postgresql-8.2dev-503.jdbc3.jar.

Can you tell me if I use the Driver in a wrong way, where I can find
the postgresql.conf file and if I need to make changes in this file?

Thank you very much for your help!
With kind regards,
Christopher Bruhn