let say you have a group of radio buttons sharing the same name attribute for sure, and upon submit or some event you want to check if one of these radio buttons was checked or not.
you can do this simply by the following code.

$(document).ready(function(){
  $('#submit_button').click(function() {
    if (!$("input[@name='name']:checked").val()) {
       alert('Nothing is checked!');
        return false;
    }
    else {
      alert('One of the radio buttons is checked!');
    }
  });
});

hope this will help you

Sometimes working on web design may not be as easy as you think.
Specially when it comes to browsers compatibility.
things get tricky and difficult with the lack of HTML CSS and Javascript debuggers like firebug on
other browsers specially IE!
plus you are working under your favorite OS, so it gets harder to test your work on different browsers and different platforms?
By surfing the web I came by chance with this incredible website LINK
How it helps you?
simply click on the link place your website address
then check the browsers you want to check under different platforms.
next you can put some rules like the preferred resolution you want the test to be ran under.
then you submit it.
Next the website will show you exactly how your website will look on the selected browsers.
it will get you results as a png images, yes images!
maybe some people wont like the service, for me if I was able to check exactly how my website looks on each browser that would be great, and maybe helps me to decrease bounce rate

give it a try