I want to make a simple jar file but I can't.

I use JBuilder 9 with SDK S40 DP2, and the issue here is that I need to make my jar file throught a ant file, and I don't know how!!!!

I can compile and run with emulator (Nokia 6230), but I can't make the jar file with the Jbuilder wizard (Archive builder)

How I do that?

Please HELP !!!!