Changing Graphics Card on a 2006 Mac Pro I have a 2006 Mac Pro running an ATI 1900XT graphics card, but since it is acting as a server (Windows 2008 R2), 99% of the time it's running headless (Remote Desktop does the job) and the graphics card is producting quite a LOT of heat (can heat a 2 liter bottle of Coke in about 40 min) I would like to replace this card with something cooler and quieter.

I am wondering is there anything that needs to be done to a graphics card that would allow it to be used on a Mac? I would prefer not to spend 2x or 3x the price of a bog-standard PCI-Express "PC" graphics card for a machine that wont be connected to a monitor all that often. I am seeing Mac-specific graphics cards (Nvidia GeForce GT 120) for about 120 EUR on Ebay, but can pick up an NVidia GeForce 210 Graphics card for 30 euros.
If you have a random low end PCI express graphics card you could probably put in any card and have it work and the most basic level. Guessing it should just work with no drivers on OS X although  it will probably be a horrible resolution and have no graphics acceleration, but it should work for when and if you need to throw a monitor on the Mac Pro when running OS X. However when booted into Windows it should be able to pick up the drivers from Windows Update or you can simply download and install drivers manually for any Windows compatible PCI Express graphics card.