Installing VMware vSphere 4 vCenter on a 64-bit Windows Server 2008 R2 is not a VMware-supported configuration yet, but it can be made to work. Scott Lowe at TechReplublic has an excellent article that discusses the issues and work-arounds <a href="http://blogs.techrepublic.com.com/datacenter/?p=1791&amp;tag=content;rightCol">here</a>.