Pick the correct glide driver (glide3x.dxe) for your 3dfx card from
one of the directories listed below and put it in the same place as
q2.exe and gl.dxe:

sst1  -> Voodoo Graphics

sst96 -> Voodoo Rush

cvg   -> Voodoo2

h3    -> Banshee, Voodoo3

h5    -> Voodoo4 and Voodoo5 (also works for Banshee and Voodoo3.)