The manufacturer of that card is NVidia. You'll find the information you need in the section for that card model on http://www.nvidia.com
To be precise, NVidia is the manufacturer of the graphics processing unit (circuitry) called "GeForce 6600...". Other manufacturer are licensed to use this curcuitry and produce their own variant of it. Asus, Gainward, Gigabyte and Sapphire are just a few examples of such manufacturers. So, when these manufacturers produce graphics cards using Nvidias GPU they market them accordingly, like "Asus GeForce 6600...", "Gainward GeForce 6600..." etc.
Another big manufacturer of GPU is ATI. They call their GPUs for "Radeon...".
All cards come in different versions. I'm sure you can find the version you need. If not, just ask someone who sells graphics cards.