I'm afraid you will have to do a bit of experimentation yourself because as I explained no-one we know has IE8..
will try to find an old install but in the meantime can you try a few things .. the markup is very basic
a wrapper 980px wide ( .wrapper ) and two columns - one 25% left floated (aside tag) , the other 75% right floated ( #maininner )(see screenshot)
perhaps the problem is IE8 doesn't understand the aside html5 tag?
could you try changing templates/flexible_lightmart/layouts/template.php line 153 to the below
<!--<aside id="sidebar-a" class="grid-box"><?php echo $this['modules']->render('sidebar-a', array('layout'=>'stack')); ?></aside>-->
<div id="sidebar-a" class="grid-box"><?php echo $this['modules']->render('sidebar-a', array('layout'=>'stack')); ?></div>
found this fix for IE6,7,8 for html5 tags
<s-cript>
for(var e,l="'article aside footer header nav section time'".split("' '");e=l.pop();document.createElement(e))
</s-cript>
you could also try adding that just before the </head> tag in the same file
both have no effect on modern browsers
remove the - in s-cript ... this is just for the forum
Cheers