Yes i do actualy
If you look certain other threads at your board it's fine now, however you're right about the thread you linked to. So i surmise now that "Dean-o" has a signature image that's marginaly to big for that very small resolution. It wouldn't effect any full width template but mediocre is set at 80% of the page width.
So if that is the issue, either ask him to change his sig image to something smaller or, you can open up the overall_header.tpl.
Then look for width="80%"
The two 10% values are the left and right margins and the 80% is the main body width. If you upped that to 90% and the two margins to 5%, it may resolve your problem also
You can try any width you like though wouldn't need to be 90%.