function validaForm(){
	var form = document.form_demonstrativo;
	
	if(form.usuario.value == ''){
		alert('Por favor, preencha: nome');
		form.usuario.focus();
		return false;
	}

	if(form.email.value == ''){
		alert('Por favor, preencha: e-mail');
		form.email.focus();
		return false;
	}
	else{
		var filter=/^[\w-]+(\.[\w-]+)*@(([A-Za-z\d][A-Za-z\d-]{0,61}[A-Za-z\d]\.)+[A-Za-z]{2,6}|\[\d{1,3}(\.\d{1,3}){3}\])$/;

		if (!filter.test(form.email.value)) {	
			alert('Por favor, preencha: corretamente seu e-mail');
			form.email.focus();
			return false;		
		}
	}
	
	return true;
}