make your movieclips for the numbers, then put something like this on them:
onClipEvent (load) {
movespeed = random(3) + 4
}
onClipEvent (enterFrame) {
this._Y = this._Y + movespeed;
if (this._Y > 500) { /////<----- that 500 is how tall your movie is
this._Y = -30;
}
that will keep them looping, from to to bottom, and their speeds will be slightly different.
also i capitalised the Y's cause they sort of morphed with the"_"
so yeah, that's a simple way to do it