a) Did you send it in to have the gfx card replaced or did it go in for something else and come back with a new card? Did they not test the card after installing it? That is very unprofessional.

B) List any strings of characters printed on the card, or better yet, slap em into google and see what comes up. (without a digi camera you either use another computer or write them down on paper)

c) Open Apple System Profiler and see what it says.

These are incredibly basic steps that pretty much anyone can manage. Please let us know what you can find.