One thing I can think of, which might not be the best solution but than again: I'm not that familliar with using scripting since I use the API, is to have 3 textboxes and set keyframes for them as well.
Fill Text1 with the text at the start of the animation, fill Text2 with the text that should be visible after the first animation end fill Text3 with the text that should be visible at the end.
Text1, with the initial text, would be visible (i.e. alpha = 100) at the start of the animation. At the end of the first part of the animation you keyframe the alpha of Text1 from 100 to 0 and the alpha of Text2 from 0 to 100, and at the end of the second animation you keyframe the alpha of Text2 from 100 to 0 and the alpha of Text3 from 0 to 100.
This way you also don't need the "waitfor".
Like I said: it might not be the best solution, but it should work.
#XPression