isnt this driver very new? tried an older one?

I just downgraded to 8.05 and I still have the issue. I also have a Geforce 2 kicking around, so I tried that, and I didn't notice any frame rate drops, although the games run at a much lower frame rate now. Using NHL 2001 as an example, I usually get ~65 fps, but then it will drop to ~45 fps momentarily, then back up to ~65. With the GF2, I was pretty steady around 20 fps. I tried using the analog vga instead of dvi, and the only difference that made is the screen doesn't turn on and off a couple times after the system boots. Just for the heck of it, I "upgraded" to 71.84, but the problem still persisted, as well as the game not rendering properly. I guess it must be something with the video card since I don't see the problem with the GF2. I only just built the machine, so I can't say if it's worked before and I don't have another machine I can test it on. I've been trying to get a hold of at least a Ti 4200, but they're not exactly easy to come by.

Update: I enabled AGP fast write in the BIOS, but that didn't stop the issue. I get much better performance now though. I played a bit of Need for Speed III with fraps running and timed the frame drops. It would run steady at 60 fps, then it would drop to about 45fps and back up to 60 approximately every 15 seconds.

Merely an idea, but do those games need the CD-ROM drive? If so, slowdown when accessing the drive?

Some of them need a CD, some of the others I've tested don't. I'm mounting iso images in Daemon Tools anyway, so it should be faster than accessing a CD. Regardless though, the problem doesn't occur with the same games with the GF2 card.

I had done a lot of playing around with drivers, so I'm wondering if that might be the cause as I don't recall it being like that after a fresh install. After perusing the forums I've come up with these driver versions to install so I'm going to do a fresh windows 98 install and only install drivers once.

GPU: nvidia 43.45 (want to eventually upgrade to a GeForce4 Ti)
Chipset: via hyperion 4-in-1 4.56
SB Live! 5.1: VXD 4.12.01.0905

If any of these don't look right, please let me know.

So after the re-install, games seem to be running fine now. I think it might be related to either DirectX 9 or something I did with RivaTuner. My card only supports DX8 and I had DX9 installed, but I don't think that was the issue, so it was probably something I did with RivaTuner. I believe I was trying to force v-sync or something, so maybe I some how broke the system. The only downside right now is that my frame rates are quite a bit lower (NHL 2001 went from ~70 to ~45), but at least they're steady.