Hmm... I dont really know netbeans, nor jarsigner specifically. I usually build with Ant or Eclipse.
If you're familiar with jarsigner and command-line building you may want to give ant a try. There are example ant build script that will take care of the signing and zipaling stuff.
Sorry, wish I could be more help. I guess as a last resort you could download eclipse and ADT and at least setup the signing process/keys through the wizard, then use ant from then on.