onRollOver problem!

I have this code, and it works great.

MC.onRollOver = function() {
this._alpha = 70;
};
MC.onRollOut = function() {
this._alpha = 100;
};

But I haven’t had access to flash for a long time, so I have forgotten alot.
What I want to is to instead of alpha, make a line around the movieclip.
The easiest way to do that is of course to make a simple button, but the buttons are dynamically (?) loaded in to the .swf, so that doesn’t work.

hope you understand my question…

thanks in advance!