CheerpJ converts Java bytecode to JavaScript. It can run applets in any modern browser without native plugins. The free version supports Java 1.5 up to a point.
In Windows, try running the installer in "Compatibility Mode" for Windows XP.
Oracle has removed all downloads for Java 5 from its official public archives. However, the Java Archive (a limited access area for developers) and third-party vendors hold copies. – verify checksums and scan every file.
If you have source code, migrate the applet to (an open-source replacement for Java Web Start) or convert the UI to a desktop Swing application accessed via VNC.
: Choose the appropriate installer for your operating system (e.g., jre-1_5_0_13-windows-i586-p.exe for 32-bit Windows).
Let's be brutally honest. Using this plugin is like leaving your front door open in a high-crime neighborhood.