Some games will automatically use the primary card for d3d. Canopus drivers let you select your voodoo cards to be used by all 3d games. Other boards do not give you a choice in drivers, and you need an external program when you are running games that do not give you a choice as to what 3d card to use. You can get a program called 3d control center that lets you chose which video card will be used for direct 3d games (you can get this on maximum pc mag's cd monthly, or from their website). This really should not be a big deal for you though, as you will likely want to use the Riva tnt for all your direct 3d and opengl games, and save the voodoo2 for glide games. The riva tnt chipset has better image quality and similar frame rates to a single voodoo2 12mb card.