Generally you can ignore the drivers of the particular brand, such as HP and just use the drivers from the GPU manufacturer, such as Nvidia.
Also, I believe the consensus is that it's best to use multiple cards of the same manufacturer, such as multiple Nvidia, OR multiple Matrox, but avoid mixing them in the same box. Also avoid ATi cards for this purpose, as they have a reputation for not being too cooperative in multiple card setups. The same may be said for windows Vista as well - seems there's a greater chance of success with XP. Also, as Gnome mentioned, a motherboard with onboard video can throw a spanner in the works as well.