The graphics drivers for these models, downloaded via the feed, do not install with a scripted install.
Thanks to Pete Danner and Irwin Koo, we found that drivers directly from nvidia do install.
Simply remove the video drivers in question from \\<ikbox>\drivers_postinstall\dell\windows_7_x64\WorkStation_T5500\video\*
Then download, uncompress these:
and add them to the video directory shown above.  These graphic drivers will install.
There are a number of times when oem drivers may not work, and downloading them from the manufacturer website is an acceptable solution.