You need to add the code to an existing part of the code. Tables will move the rest of the columns over to make room for that. put it in an existing TD or a DIV code.
Looking at the code add the following to the template where you added the current TD.
Find the following
<td style="padding-right: 15px;" width="175">
and replace it with the following
<td width="175px" style="background-image:url(images/mainbg.png); background-repeat: repeat;">
and it should work just fine

any problems let me know