I have a Duron 1300, 512MB PC133, 32MB GeForce2 MX, Windows 98 system. The Direct3D mode on 1024x768 tests at about 105fps.
Does Direct Draw or Software mode do any better than Direct3D? Did you check for updated drivers? Is there an option to disable vsync in the video driver settings?
3DMark does include very high polygon scenes, which will produce low frame rates on any system. Is there a help file or something which describes the expected performance for each of the tests? There is a feature to compare your results to other systems (might only be in the registered version), but I don't know how detailed it is.
A forum or newsgroup (
Google Groups) for NVidia (or video card / gaming performance in general) might be a good place to check, if no one else has any suggestions.
NVidia's FAQ;
[*]
How can I optimize my display drivers for faster gaming performance?[*]
I get very poor performance with my games. How can I fix this? 
