<form method="post" action="pool.php" onsubmit="//return !isNaN(this.answer.value);">
<table width="100%" cellpadding="5" cellspacing="0" class="l">
<tr><th>Нравится ли Вам мой сайт?</th></tr>
<tr><td class="pool">
<input class="pool" type='radio' name='answer' value='1' /> Да, нравится<br />
<input class="pool" type='radio' name='answer' value='2' /> Нет, не нравится<br />
<input class="pool" type='radio' name='answer' value='3' /> А мне без разницы<br />
</td></tr>
<tr><td align="center">
<input type="submit" value="Голосовать" />
</td></tr>
</table>
</form>

<input class="pool" type='radio' name='answer' value='1' checked/>

<FORM onsubmit="return checkForm(this);">
<INPUT name=radiogroup value=0 type=radio>
<INPUT name=radiogroup value=1 type=radio>
<INPUT name=radiogroup value=2 type=radio>
<INPUT name=radiogroup value=3 type=radio>
<INPUT type=submit value=Ага>
</FORM>

<script language=JavaScript>
<!--
function checkForm(f)
{
var i;
for (i=0; i<f.radiogroup.length; i++)
if (f.radiogroup[i].checked)
return true;
return false;
}
//-->
</SCRIPT>

<INPUT type=submit value=Ага>