Puoi partire da qua:
codice:
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=latin1"/>
<title>Test</title>
<script type="text/javascript">
function AddDescr(descrizione)
{
    var i, campo, found;
    found = false;
    for (i=1; i<=5; i++){
        campo = document.getElementById("TEXT"+i);
        if (campo.value == "") {
            campo.value = descrizione;
            document.getElementById("TEXT"+i+".2").focus();
            found=true;
            break;
        }
    }
    if (found === false)
        alert("Fine posti liberi!");
}

</script>
</head>
<body>

<form>
Dato 1:<input type="text" id="TEXT1" name="TEXT1" value="" />Quantit&agrave; 1:<input type="text" id="TEXT1.2" name="TEXT1.2" value="" />

Dato 2:<input type="text" id="TEXT2" name="TEXT2" value="" />Quantit&agrave; 2:<input type="text" id="TEXT2.2" name="TEXT2.2" value="" />

Dato 3:<input type="text" id="TEXT3" name="TEXT3" value="" />Quantit&agrave; 3:<input type="text" id="TEXT3.2" name="TEXT3.2" value="" />

Dato 4:<input type="text" id="TEXT4" name="TEXT4" value="" />Quantit&agrave; 4:<input type="text" id="TEXT4.2" name="TEXT4.2" value="" />

Dato 5:<input type="text" id="TEXT5" name="TEXT5" value="" />Quantit&agrave; 5:<input type="text" id="TEXT5.2" name="TEXT5.2" value="" />

<input type="submit" value="Invia" />
</form>

Penna
Inchiostro
Calamaio
Foglio

</body>
</html>
HTH
Zappa