1. You will need to download a copy of the Fetch installer. You can do so by holding down the Option key on the keyboard and (while the Option key is down) clicking here.
2. A window will pop up asking where you want to download the file. Click on the Desktop button. Then click on Save.
3. Once the file has finished downloading, you should have a file on the desktop titled "FetchInstall.sit". Double click on the file.
4. A StuffIt window should pop up asking where you want to unstuff the file. Make sure it's pointed to the Desktop and click on Unstuff.
5. Once StuffIt is done, you should have an icon titled Fetch 3.0.1 Installer.
6. Double click on the installer and run through it using the defaults.
7. And that's it. You've just installed Fetch.