Hola de nuevo a tod@s!!
Al final lo he solucionado con una funcion "intermedia"
Aquí lo dejo por si le sirve a alguien...
Código PHP:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<title>Calculadora</title>
</head>
<body onmouseout="window.status=' '" onmouseover="window.status=' ';return true">
<script language="JavaScript">
function calcula() {
var frm = document.calc;
var val1 = frm.val1.value;
var val2 = frm.val2.value;
var val3 = val2*val2;
var result1 = val2*val2;
if ((frm.val1.value>0 && frm.val1.value<99999) && (frm.val2.value>0 && frm.val2.value<99999)) {
var res = (val1*14.10)+(val2*7.05)+(result1*9.40);
frm.result.value = parseFloat(res).toFixed(2);
} else {
frm.res.value = 0;
alert ("Debes indicar valores númericos en los campos indicados.");
}
}
function suma() {
var frm = document.calc;
var val1 = frm.val1.value;
var val2 = frm.val2.value;
frm.result1.value = val2*val2;
}
</script>
<center>
<div align="center">
<table width="300" border="0" cellspacing="0" cellpadding="10">
<form name="calc">
<tr>
<td valign=top class="centro grande">Calculadora</td>
</tr>
<tr>
<td>
Valor 1 <input type="text" name="val1" size="3" maxlenght="5">
</td>
</tr>
<tr>
<td>
Valor 2 <input type="text" name="val2" size="3" maxlenght="6" onchange="javascript:suma();">
</td>
</tr>
<tr>
<td>
Resultado 1 <input type="text" name="result1" size="3" maxlenght="6" value="" readonly>
</td>
</tr>
<tr>
<td align="center">
<input type="button" class="button" value="Calcular" onClick="calcula();">
</td>
</tr>
<tr>
<td>
Totales <input type="text" name="result" size="11" maxlength="10">
</td>
</tr>
</form>
</table>
</div>
</td>
</tr>
</table>
</center>
</body>
</html>