You can't have both cards working together. This is because the RIVA is a 2d/3d card, thus handling all graphics. You will have to choose either one, but not both.
Well, for your TV output, you'll just have to abandon it, or return the Creative card and get one with TV uoput from either STB or Diamond.
But in my point of view, TV output is not really important feature. Which would you rather sacrifice, TV output or fast #D graphis? The choice is yours, but if i were you, i would defintely ditch the ATI card for the RIVA