honestly, this is one that you'll get a lot of responses both ways -- I prefer a new thread only if the old one doesn't answer your question, BUT
You hang around enough forums you'll have plenty of people who will take you to task for bumping an old thread "This is old, start a new one!" -- but at the same time you'll find an equal number who will ***** at you either "there's already a thread for this" or "don't you know how to use Google".
My advice, use your own judgement. Someone gets their panties in a wad over it that's their problem... and remember, the only stupid question is one you already know the answer to.