Xiquetam, prueba esto:
Código PHP:
<html>
<head>
<script language="JavaScript">
function validar(){
var bOk = true; nTot = 0;
with (document.Questionnaire){
for (var i = 1; (i <= 3) && bOk; i++){
if (isNaN(eval("Q" + String(i) + ".value"))){
alert("You have not type a number");
eval("Q" + String(i) + ".focus()");
bOk = false;
} else nTot += eval("parseInt(Q" + String(i) + ".value)");
if (bOk && (nTot > 1000)){
alert("Te pasaste de puntos !!");
bOk = false;
}
}
}
return bOk;
}
</script>
</head>
<body>
<form name="Questionnaire">
Primero:
<input type="text" name="Q1">
<br>
Segundo:
<input type="text" name="Q2">
<br>
Tercero:
<input type="text" name="Q3">
<br>
<input type="button" onclick="validar()" value="Validar">
</form>
</body>
</html>
Suerte.