will turn black but the game audio will still be on in the background. I have an old Ati x1900 in my mac pro and i am thinking of upgrading to an ati radeon 3780 will this fix the problem with the screen turning black while playing video games such as battlefield bad company 2? And is this graphics card the card I should get for my mac pro if i want to be able to play video games without it turning black?

x1900 would burn up and stop running with that game. Also the game wont play great with a 3780 either. Get a 60$ and up card. Nvidia or Ati. Doesn't really matter.