So you want to upgrade the video card you say. Well this one will not fit in the Mac Mini. It probably won't fit in a barebones motherboard either. It will plug into a Mac G5 tower.
Macs are expandable but they do not sell barebones. They sell plug and play.
Mac towers are expandable. Even an old Mac costs more than most of you want to spend building one. That is not Apple's problem, that is their pride. Even the old Macs have a high resale value. Apple does not set the price on used computers. Enough of the public thinks an old Mac is worth more than a new Dell. Someday you may understand and even benefit from owning a computer with a resale value.
NVIDIA Quadro FX 4500
Bring detailed worlds to life with the NVIDIA Quadro FX 4500. One of the most advanced graphics cards available, it has an integrated stereo 3D port, so scientists can use stereo goggles for stereo-in-a-window visualization applications.(2)
The Quadro FX 4500 includes hardware support for anti-aliased points and lines, accelerated clip planes, and two-sided lighting, making it an ideal choice for the most advanced design and visualization applications. And since it has two dual-link DVI ports, you can connect two 30-inch Apple Cinema HD Displays for the largest workspace with a single graphics card.