Found a great article about using the Server License Manager Script, slmgr.vbs. This is the command line method for activating and installing license keys on windows 2008 and windows 7 machines.

I needed a way to do the activation of a Windows 2008 server from a command prompt after deploying a new VM. My answer was simple, use slmgr.vbs to kick off the activation as part of the VM's customization specification. I added "slmgr.vbs /ato" to the command to run after setup and now all the 2008R2 VMs deployed from templates using that OS customization spec are working fine. I don't have to go back and activate them manually.

Check out the larger article to see some of the other great info you can pull with this.

http://www.windowsnetworking.com/articles_tutorials/Windows-Server-License-Manager-Script-slmgrvbs.html