var Centra= new Class({
		initialize: function(options){
			this.options= options;
			this.getDims();
			if(!$defined(this.options.bckg)){this.options.bckg=true};
			this.centra();
		},
		getDims: function(){
			altoTotal= window.getHeight;
			altoCuerpo= this.options.alto;
		},
		centra: function(){
			if(this.options.bckg){
				$$('body')[0].setStyles({
					'padding-top':window.getHeight()/2-this.options.alto/2 +'px',
					'background-position':'0px '+(window.getHeight()/2-this.options.alto/2)+'px'
				});
			}else{
				$('contGral').setStyle('padding-top', window.getHeight()/2-this.options.alto/2 +'px');
			}
		}
	});