yakswak-
First, when you switch from 3dfx to nVidia, or the other way around, it is best to format your hard drive and start over from scratch. Could you list exactly what games you are having problems with? No matter, 128MB in Win2K if far below what I would reccomend.
"I guess I will try to get some RAM, but it seems absurd that the Voodoo3 will run fine while the new "better" card will not."
An example using the same board on RAM. Using a GeForce DDR running UT in D3D I was all set as far as RAM was concerned(with 192MB). Switching over to OpenGL and running the Loki patch to enable S3TC textures while overall game play was OK, there would be occasional hithces when I hit virtual memory. The tradeoff was well worth it IMHO, the Loki OpenGL w/S3TC patch makes the game look a lot better. When I upgraded to 320MB of RAM even the once in a while occasional hitches vanished.
Also, I assume you are now running in 32bit color as opposed to 16bit with the V3?(A guess, not saying you are)
"Not sure whats up. May not be the same problem. I have problems on Rune, No One Lives Forever, etc... I haven't fully investigated the problem yet"
no1special-
With the V3 you can't use large textures, unlike any current board. Does that explain your problem? Maybe, I know NOLF uses large textures heavily and reccomends 256MB of system RAM using settings well below maximum.