JDBC driver problems with tomcat

Hello to everybody,
I am running postgresquel 6.5.3 and tomcat 4.0.
Everything works fine when I access databases from servlets or JSP but I
can't authenticate users with  JDBCRealms in tomcat using postgresql
databases.
If I try to start Tomcat I get this error from the JDBC driver. I am
using  the driver jdbc6.5-1.2.jar

java.lang.NullPointerException:
        at java.util.StringTokenizer.<init>(StringTokenizer.java:93)
        at postgresql.Driver.parseURL(Driver.java:240)
        at postgresql.Driver.connect(Driver.java:109)
        at org.apache.catalina.realm.JDBCRealm.open(JDBCRealm.java:548)
        at org.apache.catalina.realm.JDBCRealm.start(JDBCRealm.java:613)
        at
org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1108)
        at
org.apache.catalina.core.StandardContext.start(StandardContext.java:3334)
        at
org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1123)
        at
org.apache.catalina.core.StandardHost.start(StandardHost.java:612)
        at
org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1123)
        at
org.apache.catalina.core.StandardEngine.start(StandardEngine.java:307)
        at
org.apache.catalina.core.StandardService.start(StandardService.java:388)
        at
org.apache.catalina.core.StandardServer.start(StandardServer.java:505)
        at org.apache.catalina.startup.Catalina.start(Catalina.java:776)
        at org.apache.catalina.startup.Catalina.execute(Catalina.java:681)
        at org.apache.catalina.startup.Catalina.process(Catalina.java:179)
        at java.lang.reflect.Method.invoke(Native Method)
        at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:243)

Is there a way to use Postgresql  in JDBRealms?
Thanks in advance
Francesco Lunelli