AJ mentioned it runs smoothly in 3dfx mode. Even a single core of a more or less modern CPU should provide more than enough power for HS. The AI and especially the physics are not THAT demanding
Greatest performance I had with dgVoodoo.
Settings:
1) General tab:
Windowed: Centered
2) Glide tab
3dfx card: Other, greater (free to configure)
Onboard RAM: 128MB
TMUs: 1
Memory size per TMU: 65536kB (TMU setting I don't know how to set, I just went with a magnification of the Banshee)
Resolution: 1920x1080 (must be forced now due to lack of HD implementation)
Force bilinear filter: checked
Antialiasing: 8x
Enable Glide gamma ramp: checked
Force vSync: checked
16bit depth buffer: checked
Enable inactive app state: checked
The rest unchecked
The game will run ultra smooth with these settings on my rig, even with a full grid of poly monsters, and it'll look the best I've ever seen HS look. Looks better even than forcing AA and AF through Nvidia driver!
32-bit colors seem to break projected lights on dgVoodoo, though.