[Pug-dog&Elephant]

<input type='radio' name='top' value='top1' onchange="check();"/> top 1<br />
<input type='radio' name='top' value='top1' onchange="check();" /> top 2<br />

<input type='radio' name='bottom' value='top1' onchange="check();" /> bottom 1<br />
<input type='radio' name='bottom' value='top1' onchange="check();" /> bottom 2<br />

<input type='submit' value='Отправить' name="submit" disabled="disabled"/>
<script>
function check() {
	var top = document.getElementsByName('top')[0],
		bottom = document.getElementsByName('bottom')[0],
		submit = document.getElementsByName('submit')[0];
	if (top.checked && bottom.checked)
		submit.disabled = '';
	else
		submit.disabled = 'disabled';
}
</script>

Не работает... Кнопка не становится активной...