You may have received the following error messsage while processing the Readiness checks during the installation of TFS 2010 CTP recently: [Application Tier] TF255437: An error occured while querying the Windows Management Instrumentation (WMI) interface on the following computer:. The following error message was received: Invalid Namespace.
So I though I'd check that WMI Service is running, and it was. After searching around it turns out I needed to enable WMI Compatibility for IIS 6 under IIS. You can enable this under Server Manager in Server 2008 and change the IIS role.
I think this 'feature' has been fixed for RTM of TFS 2010.