A simple explanation how to remove an obsolete DFS namespace server from a Windows 2003 Server:

Download & Install Windows Support Tools for Windows 2003

dfsutil /unmap:\<domainname><DFSname> /ROOT:\<DFSrootserver><DFSshare>

Getting an error about:

Could not execute the command successfully
SYSTEM ERROR - The system cannot find the file specified.

See my blog entry about errors removing DFS namespace server