It really isn’t that complex. Now, I don’t know how much you actually know, so I’ll try and explain it as best I can.
> First, with the text tool selected: type something on the stage and turn that into a Button Symbol (F8).
> Now double-click on your newly created button so you can edit it.
> In the Timeline you should see three different states - Up, Over, Down, and Hit.
> Hit F6 three times so that every state has a keyframe in it.
> In the Hit state, draw a rectangle that spands the size of your text.
> Select your text in the Over state and turn that into a Movie Clip Symbol (F8). Now double click your new Movie Clip Symbol to edit that.
> You should now see a normal Timeline: Create a new layer, select the text in the first/bottom layer and copy it (Ctrl+C).
> Now on the new/top layer paste in place your text (Ctrl+Shift+V). Change the color of the text in this layer to [COLOR=DarkRed]red[/COLOR].
> With the text selected (red text), go up to Insert > Create Motion Tween.
> Still on top layer: click on frame 15 and hit F6 to insert a new Keyframe.
> Select your text (in frame 15) and in the Properties Panel you should see a color: drop menu currently at None. Select that and change it to Alpha, then change the slider to the right of that to 0% to make your text invisible.
> Next, open the Transform Panel and increase your the text size to 175%.
> Now click on the frame 15 and open the Actions Panel (F9), type this in: [AS]stop();[/AS]This script does just that, stops the animation.
> Now go back to the first/bottom layer, and click on frame 15 and push F5 to insert frames so that it matches up to the top layer.
You’re done… yeah I know, it was a lot. Test your movie out and it should work the way it’s supposed to. I also recommend increasing the frame rate (fps) to 16 so that your Motion Tweens move smoothly.