When a user clicks Show link, display the password, hide it when clicked again

you weren't using document on for getElementById

function toggle_password(target){
    var d = document;
    var tag = d.getElementById(target);
    var tag2 = d.getElementById("showhide");

    if (tag2.innerHTML == 'Show'){
        tag.setAttribute('type', 'text');   
        tag2.innerHTML = 'Hide';

    } else {
        tag.setAttribute('type', 'password');   
        tag2.innerHTML = 'Show';
    }
}

your id names are illegal and difficult to work with: pwd'.$x.' you can't have some of those chars.

The HTML 4.01 spec states that ID tokens must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens (-), underscores (_), colons (:), and periods (.).

also, this method will not work in all browsers, in IE < 9 for instance you can only change .type before the element is attached to the document

try swapping them:

function swapInput(tag, type) {
  var el = document.createElement('input');
  el.id = tag.id;
  el.type = type;
  el.name = tag.name;
  el.value = tag.value; 
  tag.parentNode.insertBefore(el, tag);
  tag.parentNode.removeChild(tag);
}

function toggle_password(target){
    var d = document;
    var tag = d.getElementById(target);
    var tag2 = d.getElementById("showhide");

    if (tag2.innerHTML == 'Show'){

        swapInput(tag, 'text');
        tag2.innerHTML = 'Hide';

    } else {
        swapInput(tag, 'password');   
        tag2.innerHTML = 'Show';
    }
}

hope this helps -ck

Here is an example using jQuery (pastebin):

$(document).ready(function() {
  $("#showHide").click(function() {
    if ($(".password").attr("type") == "password") {
      $(".password").attr("type", "text");

    } else {
      $(".password").attr("type", "password");
    }
  });
});

#showHide {
  width: 15px;
  height: 15px;
  float: left;
}
#showHideLabel {
  float: left;
  padding-left: 5px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<table>
  <tr>
    <td>Password:</td>
    <td>
      <input type="password" name="password" class="password" size="25">
    </td>
  </tr>
  <tr>
    <td></td>
    <td>
      <input type="checkbox" id="showHide" />
      <label for="showHide" id="showHideLabel">Show Password</label>
    </td>
  </tr>
</table>

Sources:

http://www.voidtricks.com/password-show-hide-checkbox-click/

How to align checkboxes and their labels consistently cross-browsers