There are always allot of questions about how volume licensing is handled. Microsoft TechNet has a great video that talks about volume activation and KMS. This video covers how KMS will work with Windows 7 and Server 2008. One of the things out of the video that I found useful is that the systems need to be able to check back in with that KMS server ever 180 days. Check out the video over there and let me know what you think.
TechNet Volume Activation Video
http://technet.microsoft.com/en-us/dd936198.aspx
