If you have a customized theme follow these instructions for bolding the titles: Go to where your threads show up in your website Highlight a thread and click view selection source in firefox Look for a HTML tag with a class If you find the class go into the vBulletin CSS editor and search for the class If there is no text decoration defined put in font-weight: bold; for the css class you found Save it and view the threads It should be bold now. Please be care ful when doing this as you won't be able to distinguish read from unread threads. You might have to markup read and non read threads with contradicting CSS so you can notice the difference.
Actually it isn't coded in CSS. If you view the source for an unread thread it would contain the markup style="font-weight:bold" while the read threads will not contain any font decoration other than what is already written for the HTML tag in this case a: in the CSS.