<div class="image-1">
    <img src="large1.jpg">
</div>


<div id="thumbs">
    <a id="thumb_1" href="large1.jpg" title="1"><img src="small1.jpg" alt="image 1"/></a>
    <a id="thumb_2" href="large2.jpg" title="2"><img src="small2.jpg" alt="image 1"/></a>
    <a id="thumb_3" href="large3.jpg" title="3"><img src="small3.jpg" alt="image 1"/></a>
</div>

...

<div class="image-2">
    <img src="large2.jpg">
</div>

<div id="thumbs">
    <a id="thumb_1" href="another_large1.jpg" title="1"><img src="anout_small1.jpg" alt="image 1"/></a>
    <a id="thumb_2" href="another_large2.jpg" title="2"><img src="another_small2.jpg" alt="image 1"/></a>
    <a id="thumb_3" href="another_large3.jpg" title="3"><img src="another_small3.jpg" alt="image 1"/></a>
</div>

...

$(function() {

    $(".mouseover a").mouseover(function(){
        var src=$(this).attr('href');
        var classs=$(this).attr('class');
        classs=classs.substr(6);
        $('.'+classs).find('img').attr('src',src);

    })

})