Help with jar

I was working with a Jar file ( postgresql-8.0-315.jdbc3.jar ). When i launched my application from the ECLIPSE it worked fine, but when i try to open it from cmd java -cp <app-dir> <package.classname> i get a ClassNotFound Exception when i try:

Class.forName("org.postgresql.Driver");

how can i fix this?.

Thnx.

[349 byte] By [Fer8484a] at [2007-10-2 22:24:56]