codice:
<script>
function controlla(f) {
var v = f.campo.value;
	rv = (v!="" && !isNaN(v));
	if(rv) {
		v = parseFloat(v);
		rv = (v>1 && v<89)
	}
	if (!rv) 
		alert("Correggi il valore");
	return rv;
}
</script>
...
...
<body>
<form ... onsubmit="return controlla(this)">
<input type="text" name="campo">
</form>
</body>
ciao