function abre_pop( url, titulo, pop_size_w, pop_size_h )
{
	var posicaoX = screen.width - pop_size_w ;
	var posicaoY = screen.height - pop_size_h ;
	
	if ( posicaoX > 0 )
		posicaoX = Math.round( posicaoX / 2 ) ;
	else
		posicaoX = 0 ;
		
	if ( posicaoY > 0 )
		posicaoY = Math.round( posicaoY / 2 ) ;
	else
		posicaoY = 0 ;
	
	pop = window.open( url, titulo, "toolbar=no,location=no,address=no,directories=no,status=no,menubar=no,scrollbars=no,resizable=yes,copyhistory=yes,maximized=yes,width="+pop_size_w+",height="+pop_size_h+",left="+posicaoX+",top="+posicaoY ) ;
}