Help with setInterval!

1

I got this MC I load. How could I put a setInterval function in front of it?

onClipEvent (load) {
    this._x = 100;
    this._y = 400;
}
onClipEvent (enterFrame) {
    if (this._y>300) {
        this._y -= 5;
    }
}

And what if I wanted to do this with several MC’s in the same movie?