All our Windows Virtual Server images have the appropriate product key baked into the build but activation is still required once the server installation is complete. This process happens automatically but when you first log into the server you will be presented with the "Initial Configuration Tasks" window which includes an "Activate Windows" step.
When you click this it will open an "Windows Activation" window which includes a Product Key input box which is blank. It is ok to leave this input box blank and click the Next button. It will confirm that you would like to activate your current key which is fine so just click OK and the activation process will complete.
If for any reason the activation process fails please contact our support team with the details of the message your Virtual Server generated.