I have this radio button group, and I would like to add an onclick function.
Ultimately, I am aiming for the selection to determine which form is shown, but for now i just need to get the form to react to the mouse clicks.

This is the code:
PHP Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Contact THT</title>

<link href="css.css" rel="stylesheet" type="text/css" />
<script type="text/javascript">
function radio()    {
                    if(document.getElementById("msg_type_0").checked == true) document.write("avl is selected");
                    else if (document.getElementById("msg_type_1").checked == true) document.write("gen is selected");
                    else (document.getElementById("msg_type_2").checked == true) document.write("fbk is selected");
</script>
</head>

<body>


<div id="container">
    <div id="titlebar">
        <div id="logo" style="float:left;">
            <img src="images/doncaster.gif" alt="tht logo" />
        </div>
        <div id="header" style="float:right;">
            <h1>Contact THT</h1>
            Send a message to the Co-ordinating Team, <br />
            or feedback about this site
        </div>
        <div id="nav">
            <?php include("nav.php"); ?>
        </div>
    </div>  
    <div id="content">
        <h3>I would like to send...</h3>
        <form id="form1" name="form1" method="post" action="">
  <p>
    <label>
      <input type="radio" name="msg_type" value="avl" id="msg_type_0" onclick="radio()"  />
      ...my availability</label>
    <br />
    <label>
      <input type="radio" name="msg_type" value="gen" id="msg_type_1" onclick="radio()"/>
      ...a general message</label>
    <br />
    <label>
      <input type="radio" name="msg_type" value="fbk" id="msg_type_2" onclick="radio()"/>
      ...feedback about the site</label>
    <br />
  </p>
</form>

        
        
    </div>
    <div id="avail">
        <form id="contact_data" name="contact_data">
        <h3>Availability</h3>
            <table width="125" border="0" cellspacing="0" cellpadding="0">
              <tr>
                <td>Your Name</td>
                <td><input name="name" type="text" value="name" size="25" maxlength="25" onfocus="document.contact_data.name.select()"/>
                </td>
              </tr>
              <tr>
                <td>Your email address</td>
                <td><input name="email" type="text" value="email" size="25" maxlength="25" onfocus="document.contact_data.email.select()"/></td>
              </tr>
              <tr>
                <td>Your phone number</td>
                <td><input name="phone" type="text" value="include the area code" size="25" maxlength="25" onfocus="document.contact_data.phone.select()"/></td>
              </tr>
              <tr>
                <td>Available as follows:</td>
                <td><textarea name="message" cols="25" rows="5"></textarea></td>
              </tr>
            </table>
        </form>
    </div>
    
</div>
</div>
</body>
</html>
Any help appreciated!