function changeImage()
{
  form.mainimage.src = form.list.options[form.list.selectedIndex].value;
}
function prevImage()
{
	if(form.list.selectedIndex == 0)
	{
		form.list.selectedIndex = form.list.options.length-1;
	}
	else
	{
		form.list.selectedIndex--;
	}
	changeImage();
}
function nextImage()
{
	if(form.list.selectedIndex == form.list.options.length-1)
	{
		form.list.selectedIndex = 0;
	}
	else
	{
		form.list.selectedIndex++;
	}
	changeImage();
}