http://support.microsoft.com/kb/974090/

An update is available that enables the operating system to take advantage of the Enhanced C1 state (C1E) for lower power consumption offered by an AMD multicore processor on the x64-based versions of Windows Vista SP2, of Windows Server 2008 SP2, of Windows 7, or of Windows Server 2008 R2
You may request them (Win7/2008R2 and Vista/2008) here: http://support.microsoft.com/hotfix/...x?kbnum=974090

I uploaded them to a file hosting site in case you don't want to request them:

Windows6.1-KB974090-x64.msu
Windows6.0-KB974090-x64.msu