Set CSS cell-spacing for TD

So I have this certain table. I know I'm not supposed to use table for layout, but in this case I'm forced to.

I need to style a specific TD's cell-spacing (the TD with the class .ritey). I know I have to target the TABLE to set its cell-spacing, but I don't want other TDs got affected. I only need to style this single TD.

Is there any way to do this?

Here is a quick rough sketch with MS Paint, I hope this explains what I need:

In the overall layout there will be multiple rows (multiple TR). In this question I only show one row. I need all columns (all TDs) to remain unchanged, except for .ritey. I want .ritey to have 10px margin around it (margin, not padding). I hope this explains better!

.

And here is what I got in my HTML. I tried td.ritey { border-spacing:10px; } but it does not seem to work.

  <table width='100%' border='0' cellspacing='1' cellpadding='3' class='postable'>
  <tr>
  <td valign='middle' class='row4 uname' colspan='2'>
  <div class='name'>
   <a href='#'>Guest</a>
  </div>
  </td>
  </tr><tr>
  <td width='100%' valign='top' class='ritey'>
        <div class='postcolor'>
         Post content
        </div>
  </td><td valign='top' class='lefty'>
    <div class='postdetails'>
    Details
</div>
  </td>
  </tr></table>

Any help is really appreciated.

See fiddle for code and demo

fiddle: http://jsfiddle.net/kDKEw/2/

demo: http://jsfiddle.net/kDKEw/2/embedded/result/

HTML:

<table cellspacing="1" cellpadding="3" border="1" width="100%" class="postable">
  <tbody><tr>
  <td valign="middle" colspan="2" class="row4 uname">
  <div class="name">
   <a href="#">Guest</a>
  </div>
  </td>
  </tr><tr style="height: 36px;">
  <td width="100%" valign="top" class="ritey" style="width: 90%; position: absolute; margin: 4px;">
        <div class="postcolor">
         Post content
        </div>
  </td><td valign="top" class="lefty" style="float: right; width: 6%;">
    <div class="postdetails">
    Details
</div>
  </td>
  </tr>
</tbody>
</table>

SS:

Updated Fiddle as per image illustration ( https://i.sstatic.net/YBXCK.png ): given by deathlock

Fiddle: http://jsfiddle.net/7xfxF/1/

Demo: http://jsfiddle.net/7xfxF/1/embedded/result/

SS: