Currently Being ModeratedSep 15, 2013 1:41 PM (in response to elliottls)
You can download the Aperture Trial installer and unlock it with your serial key:
Download it here Aperture 3.1 Trial
After running the installer update immediately from the -menu > Software Update. Then launch Aperture and enter the serial number from your installer disk.
If your Aperture version should be an upgrade from Aperture 1 or Aperture 2 you will also have to enter the previous serial numbers.