function cambiar_pagina(opt)
{
	uri = new String(document.location);
	uri = uri.substring(0,uri.lastIndexOf("/")+1)+'index.php?';
	
	if(categ != 0)
		uri = uri + 'categ='+categ+'&';
		
	switch(opt) {
		case -1: actual_page--;
				 uri = uri + "page=" + actual_page;
				 break;
		 case 0: actual_page = document.getElementById("combo_paginas").options[document.getElementById("combo_paginas").selectedIndex].value - 1; 
		 		 uri = uri + "page=" + actual_page;
		 		 break;
		 case 1: actual_page++;
				 uri = uri + "page=" + actual_page;
				 break;
	}
	location.href = uri; 	
}