Yeah MAKs are not used for setup (like a product key), only for activation after installation. You can install and activate the MAK after installation by running slmgr.vbs
Here's some more info that might be helpful: http://www.microsoft.com/technet/windowsvista/plan/volact1.mspx
Here's some more info that might be helpful: http://www.microsoft.com/technet/windowsvista/plan/volact1.mspx