Slipped my mind, but installing TFS 2005 also requires SharePoint.
SharePoint installation sucks.
SharePoint trashes out anything .NET-based that’s installed on the default web site.
Vault is a .NET product installed on the default web site. (hey! Don’t anticipate the train wreck… I didn’t have the benefit of hindsight!)
(approximately) First thing to do after installing TFS is to migrate source code to the new project.
Solution: Reinstall vault on a new web site instance (such as server:8000), and point the installer at the old databases.