hi there i have this code using a radio button to enable and disable text but for some reason the disable button doesn't work,can anyone help me?when i chose the 1st radio button the other textbox must be disabled and so on..

Code:
<html>
<head>
<title>Disable Text Box</title>
<script language="JavaScript">
function DisBox(fldobj,txtbox)
{
txtbox.disabled=eval(fldobj.value);
(txtbox.disabled==false) ? txtbox.focus(): fldobj.focus()


}
</script>
</head>
<body bgcolor="lightgreen">
<center>
<form name="Distbox">
<input type="radio" name="disb" value="false" onClick="DisBox(this,document.Distbox.txtb)">
<input type="text" name="txtb" size="30" disabled="true">
<input type="radio" name="disb" value="false" onClick="DisBox(this,document.Distbox.txta)">
<input type="text" name="txta" size="30" disabled="true">
</form>
</center>
</body>
</html>