Tu recopies dans ta partie HEAD :
</STYLE>
<style>
.shakeimage{
position:relative
}
</style>
<script language="JavaScript1.2">

/*
Script créé par 
© Dynamic Drive
Distribué par Net@scope
*/

//configure shake degree (where larger # equals greater shake)
var rector=3

///////DONE EDITTING///////////
var stopit=0 
var a=1

function init(which){
stopit=0
shake=which
shake.style.left=0
shake.style.top=0
}

function rattleimage(){
if ((!document.all&&!document.getElementById)||stopit==1)
return
if (a==1){
shake.style.top=parseInt(shake.style.top)+rector
}
else if (a==2){
shake.style.left=parseInt(shake.style.left)+rector
}
else if (a==3){
shake.style.top=parseInt(shake.style.top)-rector
}
else{
shake.style.left=parseInt(shake.style.left)-rector
}
if (a<4)
a++
else
a=1
setTimeout("rattleimage()",50)
}

function stoprattle(which){
stopit=1
which.style.left=0
which.style.top=0
}
</script>
Tu recopies ensuite ce code au sein de la balise qui appelle ton image :
class="shakeimage" onMouseover="init(this);rattleimage()" onMouseout="stoprattle(this)"