To sign an applet jar file with the Sun Java Digital Signing ID, use the jarsigner utility (included with the Sun Java JDK) as shown below, replacing "digi" with the alias you created when your certificate was requested and imported into keystore:

C:\j2sdk1.4.2\bin>jarsigner -keystore mykeystore -storepass <mypassword> -verbose myjarfile.jar digi