davemoore, you rock!
Your hunch is spot on. I switched to build 7174 and got things to work. Note: they did not work initially...the "ExactModeTimingsDVI" setting was required. Otherwise the monitor would not sync. The old driver does not seem to report any of the reduced pixel clock messages that I was getting from build 7664.
I've attached my current config file and log in case it is helpful to anyone. Just to be clear...I now have my GeForce FX5700 Ultra working with a Samsung SyncMaster 243T (a 24" LCD) at 1920x1200 over Single Link DVI with the nVidia closed-source driver version 7174. Additionally, I have seen this setup work with the Xorg open-source 'nv' driver under FC3 (test1) and now under FC4. (I hope this helps those of you doing google searches...
Now to get things going like this under Windows...wish me luck!