<style>
#button-mp3 {background-image:url('http://img413.imageshack.us/img413/5702/sound3.gif'); padding:0; line-height:0; background-position:center; background-repeat:no-repeat}
</style>

Код:

<script>
function addSpoiler_mp3(str,from,internal){
    var pos=0,pos2=0,newpos=0
    if((pos=str.indexOf("[mymp3]",from))==-1) return str;
    if((pos2=str.indexOf("[/mymp3]"),pos+8)==-1) return str;
    newpos=str.indexOf("[mymp3]",pos+8)
    if(newpos<pos2 && newpos!=-1) str=addSpoiler_mp3(str,pos+8,true)
    if((pos2=str.indexOf("[/mymp3]",pos+8))==-1) return str;
    txt = str.substring(pos+7,pos2);
    if((sepPos=txt.indexOf("|",0))==-1) return str;
    str=str.substring(0,pos)+makeSpoiler_mp3(txt.substring(0,sepPos),txt.substring(sepPos+1,txt.length))+str.substring(pos2+8,str.length)
    if( str.indexOf("[mymp3]")!=-1 && internal==false) str=addSpoiler_mp3(str,0,false)
    return str
}

function makeSpoiler_mp3(txt1,txt2){
    txt='<br /><embed type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" wmode="transparent" src="http://www.enricolai.com/FMP3/FMP3.swf" quality="high" allowscriptaccess="sameDomain" flashvars="vol=80&action=stop&title='+txt2+'&color=4f3b1d&textcolor=e8dec4&loop=no&lma=no;height=60&amp;width=260&amp;mp3='+txt1+'" height="60" width="260">';
    return txt;
    }
    
    var popup;
        function popmp3()
        {
        popup = window.open("http://klopp.net.ru/musicbox/","popDialog","height=380,width=440")
        if (!document.all)  {popup.moveTo(100,100);}
        return false
        }
        
        function tag_urlm()
        {var FoundErrors = '';
        var enterURL = prompt("Введите ссылку на mp3 файл", "http://");
        var enterTITLE = prompt("Введите автора и название песни", "Песня");
        if (!enterURL)
        {FoundErrors += " " + error_no_url;}
        if (FoundErrors)
        {alert("Ошибка!" + FoundErrors);
        return;}
    insert("[mymp3]" + enterURL + "|" + enterTITLE + "[/mymp3]");}
    
    if((document.URL.indexOf("viewtopic.php")!=-1) || (document.URL.indexOf("post.php")!=-1)){
    elm=document.getElementById("pun-main").getElementsByTagName("div")
    for(x in elm) if(elm[x].className=="post-content"){
    var post=elm[x]
    post.innerHTML=addSpoiler_mp3(post.innerHTML,0,false)}}
    if(form=document.getElementById("form-buttons"))
form.getElementsByTagName("tr")[0].insertCell(17).innerHTML="<img src='/i/blank.gif' title='Загрузить mp3' id='button-mp3' onclick=\"popmp3(); tag_urlm()\">"
</script>