Google Chrome

When you click on a tour to download, look at the lower left of your screen and you will see the downloaded file.




Click the little dropdown arrow on the right.
Check "always open..."
Click "open" and it will open Google Earth
then start the tour automatically.
Opera

When you click on a tour to download, a window will pop up asking what to do with the file.  Click "Open".
Mozilla Firefox

When you click on a tour to download, a window will pop up asking what to do with the file.  Click "Open with" then click "Browse" then click "Google Earth".

Internet Explorer

When you click on a tour to download, a window will pop up asking what to do with the file.  Click "Open".

If the file doesn't open up in Google Earth automatically, then a window will open up with a "doc" file.  Double click to start the tour in Google Earth.
Apple Safari

When you click on a tour to download, a window will pop up asking what to do with the file.  Click "Open".

Safari will ask you a second time if you want to open the file.  Of course you do, so click "open" again.