Did you check "Blend Transparency" in the materials presets? If you didn't your preview window in the material editor will appear with a ghost image as well. If you are using a transparency to make the space around your letters show through remember the transparency mask goes into the second window of your picture texture. It's also a good idea to make sure this mask is all white and black. Grays give you half transparencys. Walk through your keyframes from beginning to end to make your changes. clicking settings in the middle can affect the settings in the previous frame. You may go back to the final frame because you changed settings out of order and find the program somehow changed the transparency setting in the keyframe from 100 to 50%. This could be your "ghost". I just did three seperate animations for a star wars takeoff. Do you have anything behind the letters that has to show through? If not try this method. I used both 2D plains and terrains. I created blue text on a black background from an image and applied it with 100% diffusion and ambience. This filled the camera view. I created four keyframes of the text at 0, 40, 120, and 160 frames. I went to the 0 and 160 keyframes and set diffusion and ambience to zero. I rendered the whole thing regular normal AA because super fine anti alias kept chopping bits out of the letters no matter where I positioned the camera. The text fades in lingers between 40 and 120 and fades back out. This text doesn't actually turn transparent, the object just goes black on a black background. It takes 1/20th the render time as an actual transparerncy takes. Hope this helps:)