how to create an applet java in eclipse from a project whichs depends from a jar file?

[welsungo]

I've got an applet java written in eclipse and the project depends of
an external jar file. I want to export my project, with the jar file
in, of course, to a new jar file so i can launch it from a web page.
When i set export in eclipse, i select java class files from my
project, and i select also the jar file from which my project depends
on and they all are set in a new jar file. But... when i run the web
page, it runs the exceptions java.lang.NoClassDefFoundEffor because
java isn't found my external class file.

what have i done bad?

thanks.