2
You could easily use that design. You could just not use the right colum and keep your left and center columns the same width.
If you're willing to modify your templates to get a nice style (like the one your site has) then remember you can get creative and move your block areas around in html and provide some looping with smarty.
Here is simple theme.html hack which will let you line up blocks in a row.
theme.html
<table border="0" cellpadding="0" cellspacing="0">
<tr>
<{foreach item=block from=$xoops_lblocks}>
<{include file="mytheme/theme_blockleft.html"}>
<{/foreach}>
tr>
table>
mytheme/theme_blockleft.html
<td>
<{$block.content}>
td>