A colleague of mine pointed me the following facts:

• Windows 2008 RTM does not support Windows 7 as KMS clients
• Windows 2008 RTM + SP2 + KB968912 does support Windows 7 as KMS clients
• Windows 2008 (in any version) does not support Office 2010 KMS clients
• Windows 2003 does support Office 2010 KMS client (with the Microsoft Office 2010 KMS Host License Pack)
• Windows 2008 R2 supports both (probably the Microsoft Office 2010 KMS Host License Pack is required as well)

So there are two options: Windows 2003 based KMS or Windows 2008 R2 based KMS.

Reference: Microsoft Volume Licensing: Product Activation

It seems like there is some graphical tool to manage or check KMS statistics: “Volume Activation Management Tool (VAMT) 2.0”, I’ll definitely try this one out if I find some time.

A screenshot from VAMT from the Manage Activation Using VAMT 2.0_White Paper 

[update 9/06/2010] The following URL is a reference for KMS related stuff: Volume Activation Deployment Guide