Using a movieclip as a button is pretty simple. There really isn't much difference. The main thing you will need to do is add the following code.
instance.buttonMode = true;
The above code will simply create the mouse cursor behavior expected of a button.
From there, everything else is pretty much the same.
Say, you want your text to appear above the movieclip, since movieclips have their own timeline, you could place this text on frame 10 or so. Then, when you add an event listener to the symbol for a ROLL_OVER, you just say gotoAndPlay(10);
Being a movie clip, anything else you place on the movieclip's timeline will not affect this roll over. Meaning, rolling over the area where the text will appear will do nothing. Using movieclips will also open up a lot more possibilities. You can do pretty much anything you want.
I attached a simple file exampling how to do a very basic rendition of what you are wanting to do. Notice that I put a couple stop(); actions on the movieclip's timeline. You could actually do all of the code inside the movieclip itself. But, I juts put it on the main timeline for this purpose.