Help with transparency/animated text

Hello, quick question so hopefully someone can help.

I want to make an image with a transparent backround, and I want my text to be half on the image/half on transparent part and have it animated from one text to another. My problem being when it goes from one to the other after being saved you can see white edges where it's fading into the new text, any way to get rid of this? I'm using PS C4

 

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Transparency : http://sythe.org/showthread.php?t=693573