Hi hoechst,
To install:
Assuming you are using XP, the save game folder can be found at: C:\Program Files\Digital Jesters\Frogwares\The Case of the Silver Earring\save
The save files are in picture format.
Make a note of the last numbered save game.
Save the file to your desktop, and renumber it so that it sequentially follows the last file in your game. i.e. if your last save is 0010.jpeg, then renumber the save sent to be 0011.jpeg.
Copy and paste the file from your desktop into your save game folder along with all your other saves.
Exit all folders
Start up the game as usual, and load the new save. You may need to scroll through all your saves to find the new one.

, let us know how you get on.