Riva Tnt and 3dfx Voodoo 1 card

My computer contains both the riva tnt card as well as a Voodoo 1 card.
I read that glsetup supports both.
Which one will it try to install the driver for? Will it cause a conflict?
Should I use the Voodoo 1 card and swap out the Tnt card with one that is not listed and leave the Voodoo 1 card in?