Here's an easy one...

1. Download and mount the Java Update.
2. Copy the file JavaPantherUpdate.pkg to a writable partition (your desktop will work fine).
3. Use the Contextual Menus to "Show Package Contents".
4. Locate the file within the package: /Contents/Resources/Volume Check
5. "Volume Check" is a perl script. Open it in a plain text editor (I recommend the terminal app. "pico")
6. Within the first few lines of this script, locate the line:
   if (CheckVersion("$SYSTEM_VERS", "10.3", "ProductVersion", "<" ))
7. Simply change 10.3 to 10.1 to allow the update to install under MacOS 10.2.x.
8. Save "Volume Check" as plain text and run the installer!