change textbox value on start/end event by VBA

Hi,
I have 10 textbox in one slide that animated (fade in and out) automaticly in about 2 sec of delay between them, so after few seconds the screen is almost full with at least 5 textbox that not faded out yet, and then each animation repeat 70 times.
Now, I'd like to change the text (taken from a xml/xls... file) each time the animation start or end.

I have programming experience with access but never did it in powerpoint.
I guess I have to look for capture the animation event on the begining or the end and the change the text value.

I will be grateful for help

anyone ??