tdfx_dri.so:  This is the DRI module for Voodoo3 cards.
              You must also have DRI-capable Glide3 for the Voodoo3 installed.

tdfx_voodoo5_dri.so:  This is the DRI module for Voodoo4 and Voodoo5 cards.
              To use it, you must replace the tdfx_dri.so for Voodoo3 by
              copying this version on top of it:

              cp tdfx_voodoo5_dri.so tdfx_dri.so

              Then, be sure you have the DRI Glide3 for Voodoo4/5 installed.

Glide library packages for Slackware may be found in /contrib/3dfx/.