Bless you, JND !
Recompiling the drivers under 2.4.18_19.8.0 did the trick. The new (4191) driver loads and runs just fine ! As you mentioned, repaint performance isn't great and is particularly noticeable when dragging a window.
The only problem I have now is that the refresh rate is way too high for the monitor I'm using (it's a Sun branded Sony Trinitron GDM-20E20). I had to plug in another monitor to see the desktop. I changed the monitor setting using RedHat's desktop app. and restarted X but it insists on picking a bad refresh rate. I've dabbled with XF86Config settings before but without much success. Do you have any ideas about (a) how to find out what the max refresh rates are for my monitor and (b) what to put in XF86Config ?
Thanks again for teaching me nVidia fishing :-)