problem with the Tomcat

I have PostgreSQL 7.3,jdbc driver pg73jdbc2.jar
 (located in /usr/java/local/lib), J2SE 1.4.1 and jakarta-tomcat-4.1.18.
I'm using from a project.
I have a problem with the Tomcat, therefore any
application in servlet and jsp that I make it does not
find driver of the database and the one exception
that it appears is only this:
"Exception! java.lang.ClassNotFoundException: to org.postgresql.Driver at to org.apache.catalina.loader "
or Class.forName() throws ClassNotFoundException so you will need you catch and handle it.
Although to have made right everything that is necessary in the Tomcat when to the use of database.
 Since already I thank the aid of all.