The Apple-firmware 5770 works in all models of Mac Pro, but slightly more slowly in the 2006 and 2007 models that have only PCIe 1 slots.
This card came out after the 2009 model shipped. Apple only tests in shipping systems, so they will never affirm that this works in the older models.
Drivers are available in 10.6.5 and later.
An awful lot of older graphics cards have been failing after being in service for many years. It may be a problem in your Mac, or maybe not. An appointmet at the Genius Bar for an evaluation is free, in-warranty or out. Apple wants you to be a happy customer, if possible.
Thanks. This helps. So I have to upgrade to 10.6.5. Hmm...that means I have to buy a workable video card in order to see my upgarde to 10.6.5, which will allow me to install the 5770 drivers. That's a lot of money!
Maybe I should just buy a new computer...I hear Windows 8 is great (I'm being bitter).