Install Remote Desktop Connection (RDC) 6.1 on Windows Server 2003

This is not a supported solution from Microsoft, but while on a call with Microsoft this was used by the technician to upgrade the terminal services client to RDC 6.1:

Download the RDC 6.1 installer for Windows XP.

Right click on the installer, select properties, and setup compatability mode for Windows XP.

Install.