Up until about Forceware 75 (version varies by OS) all TNT and Geforce cards were supported. I say all but there are possible issues with obscure implementations like some of their rarer onboard efforts.
Around Forceware 75 they dropped support for all TNT cards, all Geforce256 and all non-MX Geforce 2's. The Geforce 2 MX continued to be supported as there production life was so long. If you have one of these cards, the 71 series is the latest with official support.
Windows 9x/ME was dropped during Forceware 80.
During the release life of the Geforce 95 series support for all other Geforce 2s, Geforce 3s and non-MX Geforce 4s was dropped. For one of these cards, the 96 series will be the latest.
Windows 2000 was also officially dropped from the 2k/XP driver around the same time meaning that although you can get the driver working, the control panel doesn't work. Why they came up with the new control panel I really can't explain. It does less than the old display properties dialogue, more than doubles the download size and doesn't work on Windows 2000. Draw your own conclusions.
They seem to have very recently dropped the Geforce FX series although not properly acknowledged it. The latest Linux driver is incompatible with the FX5600 I have tried it with.
nVIDIA's driver pages aren't always that great. In particular some of their local sites show different drivers as being appropriate for different systems. Their Linux pages are better however, this does something to explain it all:
Linux IA32
Latest Version: 177.82
Latest Legacy GPU version (71.86.xx series): 71.86.06
Latest Legacy GPU version (96.43.xx series): 96.43.07
Latest Legacy GPU version (173.14.xx series): 173.14.12
http://www.nvidia.com/object/unix.html
So there we see the four tiers of support, Geforce 6-GTX, TNT-Geforce 2 Ultra, Geforce 2 MX-Geforce 4, Geforce 4 MX-Geforce FX.