Downloadable Lunar Calendar and Windows XP Issue
Now, if you don't have a JRE installed, the following problem will show itself on Windows XP computers.
When you try to download the luca.jar file from the Downloads Page, Windows XP automatically renames it to luca.zip, and when you double-click it, as advised, it just shows you the contents of the package - nothing of interest for you.
If you want to run this program, remove the luca.zip file, download and install the JRE and then download another copy of Lunar Calendar. This should work well.
For the future, I will have to avoid creating Java programs despite of all their benefits.