StreakEagle,
Your not using your ATI to its full potential !
First of all, I'm guessing the only reason why your FPS increased only by a few more frames is because its locked to the moniter vertical refresh rate, which is typically between 75 and 85 herz !
Thats why you had aproximately the same FPS levels at lower resolutions as well as the highest resolutions (1600x1200x32).
Second, the reason your ATI may be crashing is either you do not have the latest ATI drivers (try the "catalyst" drivers, they work fine for me with aces high) or, you did not uninstall the previous drivers properly.
Personally, I do a complete OS reinstall when i switch video cards, just to make sure there are no hidden remanents of previous card drivers in the registry and ini files of windows.
You can tell I don't take vid card switching too lightly...
If you still want to keep the current OS on your system, I'd recomend you use a good registry cleaning program like "regcleaner" to find and delete all the 3dfx registry entries.
Last but not least, a few words about the ATI Radeon 8500 128MB:
It has the same clock and RAMDAC speed and almost the same performance of the GE-Force 4 ti4200 card.
The "ti" series cards are only slightly faster in "DIRECT-X" api's (which is what AH, & WW2OL are written for), but when it comes to "OPEN-GL" ATI's radeon leaves its contemporary geforce cards in the dust !
I play IL-2 Shturmovik on Open-GL at 1600x1200x32 with all bells and whistels turned all the way up and get over 100 FPS with monitor refresh rate unlocked...
In summary, don't dispair, read well into the vid card installation and driver issues, ATI is a very good card , and imho the best "bang for the buck" when it comes to games.