Windows (tested on XP and 7)
The process for Windows XP and Windows 7 is similar. These screenshots are from an XP installation.
- Plug in your board and wait for Windows to begin its driver installation process. If the installer does not launch automatically, Navigate to the Windows Device Manager (Start>Control Panel>Hardware) and find the Arduino Leonardo listing. Right click and choose Update driver.
- If prompted to search for drivers online, choose "No, not this time". And click Next
- When asked to install automatically or from a specific location, select "Install from a list or specific location" and press Next
- Choose "Search for the best driver in these locations", and check the box "incude this location in the search". Click the Browse button and navigate to your Arduino 1.0.1 or later installation. Select the drivers folder an click OK
- Click Next
- You will receive a notification that the Leonardo has not passed Windows Logo testing. Click on the button Continue Anyway
- After a few moments, a window will tell you the wizard has finished installing software for Arduino Leonardo. Press the Finish button
Original article found on arduino.cc