This will give you an idea..
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Gissa numer</title>
</head>
<body>
<form action="" method="post">
<input name="guess" type="text">
<input name="knapp" type="submit" value="Guess">
</form>
<script type="text/javascript">
document.forms[0].knapp.onclick = function() {
var theNumber = document.forms[0].guess.value;
if (theNumber>=0 && theNumber<=100) {
return true;
} else {
alert("You don't know how to follow instructions, moron!");
return false;
}
}
</script>
</body>
</html>