While wandering near-aimlessly across the various driver downloads, I finally found a comment in a readme file that points to the 7174 release as the last one that supported my Quatro2 Pro.
I downloaded and installed that without a hitch. I made the recommended changes to XF86Config, and loaded the Dell 1905FP INF file from Windows.
Things are working very nicely now, thank you very much. Digital video is cool.