Se ho capito bene...
codice:
...
<head>
<script>
function show(field) {
if (field == 'rb1') {
document.getElementById('rb1text').style.display = 'inline';
document.getElementById('rb2text').style.display = 'none';
}
else {
document.getElementById('rb1text').style.display = 'none';
document.getElementById('rb2text').style.display = 'inline';
}
}
</script>
</head>
<body>
....
<input type="radio" name="rb" id="rb" value="rb1" checked="checked" onclick="show(this.value)" value="campo1" />
<input type="text" name="rb1text" id="rb1text" />
<input type="radio" name="rb" id="rb" value="rb2" onclick="show(this.value)" value="campo2">
<input type="text" name="rb2text" id="rb2text" style="display:none" />
Ciao