Prova a fare cos (sostituisci la funzione e l'array):
var numberslide=new Array()
numberslide[0]=["IMAGE-1.jpg", "", "Descrizione 1!"]
numberslide[1]=["IMAGE-2.jpg", "", "Descrizione 2!"]
numberslide[2]=["IMAGE-3.jpg", "", "Descrizione 3!"]
function changeslides(which)
{
var imghtml=""
currentindex=(which=="initial")? 0 : parseInt(which);
var mode=(which=="initial")? "initial" : "";
var which=(mode=="initial")? numberslide[0] : numberslide[which];
if (which[1]!="")
{
imghtml='<a href="'+which[1]+'" target="'+mylinktarget+'">';
}
imghtml+='<img src="'+which[0]+'" border="'+imgborderwidth+'">';
if (which[2]!="")
{
imghtml+='<p id="descrizione">'+which[2]+'</p>';
}
if (which[1]!="")
{
imghtml+='</a>';
}
if (mode=="initial")
{
document.write('<div>'+imghtml+'</div>')
}
else
{
document.getElementById("imagecontainer").innerHTML=imghtml
changecolors()
}
}