Another blogpost about KMS again. Before this 2 other blogposts where available, just have a look at that one also:
Key Management Services (KMS) explained
Using KMS Client Setup Keys during deployment
When setting up KMS a Windows Server KMS key can be installed at first try. When using a Office (2010) key afterwards an error message is displayed.
Error: 0xC004F050 The software licensing service reported that the product key is invalid
This because the Microsoft Office 2010 KMS Host License Pack must be installed first. It can be downloaded at this location: Download Center. During installation the Office 2010 KMS key can be imported succesfully.
More information can be found on Microsoft TechNet also.