[walik]

<input type='radio' name='top' value='top1' onchange="check();"/> top 1<br />
<input type='radio' name='top' value='top2' onchange="check();" /> top 2<br />
 
<input type='radio' name='bottom' value='bottom1' onchange="check();" /> bottom 1<br />
<input type='radio' name='bottom' value='bottom2' onchange="check();" /> bottom 2<br />
 
<input type='submit' value='Отправить' name="submit" disabled="disabled"/>
<script>
function check() {
    var top1 = document.getElementsByName('top')[0],
        top2 = document.getElementsByName('top')[1],
        bottom1 = document.getElementsByName('bottom')[0],
        bottom2 = document.getElementsByName('bottom')[1],
        submit = document.getElementsByName('submit')[0];
    if ((top1.checked || top2.checked) && (bottom1.checked || bottom2.checked))
        submit.disabled = '';
    else
        submit.disabled = 'disabled';
}
</script>