How to Install PostgerSQL_Driver ( in tomcat ) ?

Dear All

I'm using :

Microsoft Windows Xp
Apache-tomcat-6.0.14
Java version  1.5.0_14
+
PostgreSQL 8.2
and
postgresql-8.2-507.jdbc3.jar

every time I wana run myApp.class I should type :
java -cp postgresql-8.2-507.jdbc3.jar . myApp

there is no problem . but when I import myApp into myJSP.jsp , tomcat brings this Error :

javax.servlet.ServletException: java.lang.NoClassDefFoundError

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I Tried to  :
1. add a classpath=add/postgresql-8.2-507.jdbc3.jar; to env-variables
2. add the jar file to jre/lib/ext
3. add the jar file to myWebApp/WEB-INF/lib
4. add the jar file to tomcat/lib

but non of them works !

would you please help me(I'm a java beginner!)

Thanks alot
Moein
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