The right navigation menu does that. The standard vbulletin theme is table based instead of css based, so you cannot make it smaller, the page will simply show a horizontal scroll bar. The right menu bar is simply not considered to be an ad. I am guessing the people that have this problem are using 1024x768 monitor resolution. (still the most widely used)
I see it too when I switch back to that res.
The only thing that would fix your issue is getting a wider monitor with more horizontal resolution or changing the resolution on your current monitor to a higher setting, which will make everything look smaller.
There are some FF plugins around that allow you to tinker with the html on a site and tweak it to your liking, but that's probably more hassle than it's worth.