function goto(id, t){
            //animate to the div id.
            $(".slider_inner_slide")
                .animate(
                    {"left": -($(id).position().left)}, {
                duration: 1000,
                easing: 'easeInOutCubic'
            });

            // add active class to the current link
            $(t).addClass('active');
        }

<div class="slider_wrapper">
<div class="slider_static-img"></div>
<div class="slider_inner_slide">
<a href="" onClick="goto('#slider_right_box', this); return false" class="active">
    <div id="slider_left_box">
        <div id="slider_left">
            <div class="slider_box_vert_mid">
                <h1>Headline</h1>
                <p>Mauris consectetur, ante quis mollis aliquet, neque magna fringilla est, in blandit magna justo sit amet purus.</p>
                <button>Registrieren</button>
            </div>
        </div>
        <div id="slider_left_rest">
            <div class="slider_box_vert_mid2">
                <h1>Headline2</h1>
                <p>Mauris consectetur, ante quis mollis aliquet.</p>
            </div>
        </div>
    </div>
</a>
<a href="" onClick="goto('#slider_left_box', this); return false" class="active">
    <div id="slider_right_box">
        <div id="slider_right"></div>
    </div>
</a>
</div>