i remember i once saw in the 3dfx tools on win98 on a friend's voodoo4 and option of 3d stereo...
but he doesnt have 3d glasses, and when we turned the option on, it didnt seem to work...
is there a way to make 3ds work on voodoos?

3D glasses do work with the voodoo5, but not through the driver option.  
I personally use wicked3d's software which works really well on quite a few games.

Well never tried mine on my Voodoo5 but in theory :
In the driver you need to enable the setting (reboot required) then shut down, connect the glasses and reboot.

is it using the page flipping method- splitting the screen in two images and the glasses make it 3d ?