I think that _moveTo is only for the drawing functions, such as drawing lines, shapes and whatnot. What I would do is:
ActionScript Code:
onClipEvent(enterFrame){
if(Key.isDown(Key.LEFT)){
this._x-=5;//or whatever your speed is
}
if(Key.isDown(Key.RIGHT)){
this._x+=5;//or whatever your speed is
}
if(Key.isDown(Key.UP)){
this._y-=5;//or whatever your speed is
}
if(Key.isDown(Key.DOWN)){
this._y+=5;//or whatever your speed is
}
if(this._x>=Stage.width+this._width){
this._x=0;
}
}
I think that should work (I have flash on a different computer so I can't test it right now).
I hope that solved your problem.