Unfortunately, it seems to be the case that many people are not satisfied with their Geforce's 2D display at the higher resolutions 🙁 Someone suggested putting the refresh rate down to 75Hz, but I see you already have that refresh rate. It's a shame really, if it wasn't for Nvidia's bad rep for high res 2D work, I probably would have upgraded my Voodoo 3 for a Geforce 2 a month or so ago.
I think you'll probably find that your card is not defective, and that it's a common problem...sorry.