I also experience the same problem. I've got a GF4 Ti4400 on a ECS mobo with VIA chipset, and I experience random crashes.
I've been fiddling around with some settings and disabling fast writes and side band addressing seemed to have improved it a bit but still not solved it.
One way for me to lock it up every time again is visiting www.ecs.com.tw
using Konqueror. I don't have that problem when using Mozilla, but with Konqueror it always locks up somehow.
That would lead to the idea that it does have something to do with fonts or the like.
Anyway, when is a nvidia-guy gonna share his thoughts with us on this problem?