We had some problems.  It seems that nobody knows what the data-tier server for TFS was.  Well it's easy to find out.

Go the your TFS application server and start Explorer.  Browse to "X:\Program Files\Microsoft Visual Studio 2008 Team Foundation Server\Web Services\Services" where X is your installation HD.  Hier you find the web.config.

Open the web.config and you will see your connectionstring to the TFS instance of your data-tier.