The script in the tutorial for creating the native jar in the Java Webstart Tutorial gave me a command to type in cmd. I tried it and it didn't work, saying the command didn't exist. Is there another way to compile the native libraries into a JAR?
There is a way, but then you'll just have the same problem moments later with the keytool and jarsigner applications.
Instead, find the jar, jarsigner, and keytool applications in your jdk's bin directory, and run them by specifying their full path instead of just "jar" or "keytool" or "jarsigner".
Alternatively you can add the jdk bin directory to your system or user PATH variable, so the commands can be found without specifying their full path.