Where do I enter the Windows Server 2008 key after installing it?

When I installed Windows Server 2008 I didn't have the (activation) key. Now that I have it I can't find where to enter it. Anybody know?

From stackoverflow Guy

• Go to Control Panel\System and then under Windows Activation click "Change Product Key".

  From Bryant

• I know in Vista this is done from the system control panel. I would check there in Server 2008.

  From Joshua Hudson

• There might be an icon down in the tray, or it will prompt you during logon. I don't recall how long it will take to prompt you, or if it takes any time at all.

  Try rebooting and logging on.

  From $pageUsers[$post.author].name