How Did They Do That?

i found this SITE that has a looping afect I'd like to use in other ways. the loop is the scrolling background I have all so found this here in flash kit
onClipEvent (enterFrame) {
if (_root.mainVar == 0) {
homeX = (-_root._xmouse*2)+1050;
} else {
homeX = (-_root.mainVar*2)+1050;
}
thisX = _x;
diffX = homeX-thisX;
if (_root.mainVar == 0) {
moveX = diffX/30;
} else {
moveX = diffX/5;
}
_x = thisX+moveX;
}
this gives the scrolling afect with out looping the clip around and around

can some one help me find a way to do what they did in the site listed.
thanks josh