I  know how others do it, but i do this. I take the  animation into PSP and create the text on top of it as vector.

I fit the text to the animation, then I  convert it to raster layer.

Keeping only the text layer activated you I go select all......float.......defloat, and this selects the text, then I go Selection/invert.

Now x out the text layer , and hit delete or cut, on each of the animation layers.

This leaves you with the animation in the shape of the text. Save this to your desktop, call it something LOL.

Highlight the text layer only, and take it into AS, duplicate it til you have as many layers as there are animations. Select all.

Now open the animation you saved in As, and  select all/Copy

go back to the text frames and paste into selected frames

there youre done.

If you want to do it all in PSP, you can duplicate all the text layers there, and merge text and animation in pairs. then you can add whatever you want like drop shadows etc.

You will find all tuts do thos by pasting each layer seperately into AS as new frames, all of which takes forever.

Once you get used to my method, it takes no time at all.

if you are repeating something a lot of times, like cutting the text shaped animation, you just need to cut the first one, then keep hitting ctrl Y for each repeat cut, that speeds up things considerably