//限制某区域id下的img的宽度
function resize(NewWidth, id) 
{
	if( !id )
		var obj=document.getElementsByTagName("IMG");
	else
		var obj=document.getElementById(id).getElementsByTagName("IMG");
	 
	for(var i=0; i<obj.length; i++)   
	{
		var image = obj[i];
		if(image.width>0 && image.height>0)
		{
			if(image.width>NewWidth)
			{
				obj[i].style.width=NewWidth + "px";
				obj[i].style.height=(image.height*NewWidth)/image.width + "px";
			}
			else
			{
				obj[i].style.width=image.width + "px";
				obj[i].style.height=image.height + "px";
			}
		}
	}   
}