Like EMF, I have a computer not hooked to the internet on which my son plays games. It has a Voodoo 3TV Card, which is supported, but is not hooked up to the internet. Since 3dfx is out of business, I cannot get any new opengl or 3dfxgl files from them or any new glide applications that come out. How about making each file separately downloadable for different video cards. That shouldn’t be too much trouble, and would be a big help.
The best thing to do is to go to www.voodoofiles.com. There they have the latest betas of the Voodoo series drivers for download, along with better OpenGL/Glide wrappers (WickedGL, etc). I don’t know how you would go there without an Internet connection, but I’ll leave that part to you. 
Same thing as Fear said but also try
http://www.3dfx.com/downloads.htm
the site is still up and it has several drivers available for voodoo cards.
The drivers are large but get a friend to download them and put them on a cd for your son. downloading at a library will not help since you would need to take them home…
You could install a cheap modem and get a free internet access service like Netzero.com or Juno and the disconnet the service if access to the net by your son is something you don’t want.
Luck,
abel