As movement help

okay, im using the movent using actions script with this code:
onClipEvent(enterFrame) {
speed = 1;
this._x += speed;
}

but, i want to make it so if the object gets to the end of the stage, it goes back to start… how can i do this?

and then, i want to make it so when u click it, it blows up, so when u click it, it switches movie clips. Any idea how?

thanks in advance