Nvidia put 12.41 drivers on their web site yesterday. They contain optimizations for SSE2 and 3dNow. They are for win2k specifically, but my guess is win9x drivers are there too.
I ran AH for a while today using them. I didn't notice a huge fps increase, but I was running 12.10s before.
(I did see one blue flash, but setting mip mapping to high quality again fixed that.) This driver also seems to have fixed the strange flashing around the wakes of the ships.