This is how you can download the bonus game for "Building cars with Gary Gadget":

If you have a PC:
Click on the sign that says "PC". When the download window appears choose "save". Choose the folder "My documents\Viva Media\Gary Gadget\Building Cars\Plugins" to save the file. If you installed "Building Cars..." in a different folder you need to put it in the folder where you installed the game. Then open this folder and double click on the downloaded file to unzip it. After that there should be two new files named "plugin.cst" and "66.dxr" in that folder.
Now you can start "Building Cars..." again.

If you have a Mac:
Click on the sign that says "MAC". When the download window appears you just choose "save". Choose the folder "My documents\Viva Media\Gary Gadget\Building Cars\Plugins" to save the file. If you installed "Building Cars..." in a different folder you need to put it in the folder where you installed the game.. After the download the packed file should extract itself in the folder (If it doesn't work double click the file. If it still doesn't work you might need software called "StuffIt Expander".)
After that there should be two new files named "plugin.cst" and "66.dxr" in the folder.
Now you can start "Building Cars..." again.

While the game is running:
Here’s how to access your new bonus game. After you’ve started the playing again you need to take your car out for a drive. You’ll see a sign on the road that says to "Blue Lake" or to "Ferrous field". If you go to "Ferrous field" you’ll find your cool bonus game. Have fun!