Animating a MC with script

Hi, I am trying to create a sliding photo gallery, this involves two buttons left and right. I have converted the photos to one movie clip so in effect i just want to animate a single object. At the moment the when you click the right arrow the clip jumps, i would like it to animate to a certain point, can anyone help, so far i have this code

on(press){

setProperty(this.gallery_mc, _x, +10);

Thanks in advance

}