A JAR file is nothing more than a "standard" .ZIP file. Use a zip-based program, put all your class files and resources inside a .ZIP file. when done, rename it to .JAR.

How to Extract a JAR File. While running your business, you may have to deal with JAR files, which are archives that compress several files into one. Though JARS are based on the ZIP compression ...

Windows ME/XP/2003 have built in ZIP file support. It is therefore, very easy to make and extract ZIP files using these operating systems.