Hey guys. Thanks so much for all your assistance.
My niece has an older computer with a ASRock P4i45GV motherboard with a 2.4ghz intel processor. I've done enough research into video cards, but there isn't that much information concerning this motherboard, specifically when it comes to more recent info.
I've learned that the agp slot is better for this than the pci slots, so I've picked out a card that should work with windows and the more frequently used Linux O.S., Ubuntu. Of course, being a Linux box most of the time, it has got be a nVidia card.
I'm wondering what you all might think about the budget minded choice that I've made.
Here it is:
3D Fuzion 3DFR66256 GeForce 6600 256MB 128-bit DDR AGP 4X/8X Video Card - Retail
Thank you all so much.

Kir_b