Firstly, you have to understand what the underlying table is doing, so just strip out, or comment out all the .css.
The you can see where your comment box should be in relation to the rest of the table.
Once you have that, just put a nested table into the correct cell (the one currently with the class "left content")
i.e. from
HTML Code:
<table>
<tr>
<td class = "leftcontent">this is where the div content has been overlaid</td>
</tr>
</table>
to
HTML Code:
<table>
<tr>
<td class = "leftcontent">
<table>
<tr>
<td class = "whateverstyle">
type your content here rather than in the div
</td>
</tr>
</table>
</td>
</tr>
</table>
then the remainder of the .css can be replaced with the exception of the div content, which you can now insert directly into your nested table.
HOWEVER - I don't see the need to split these cells - why can't you just put your content intot he cell and use styling on the <td>'s? You may have to clarify your problem a bit.
Hope this helps a little to start off with.