I agree with Rachel. To take him downstairs or let him sleep in the playroom is giving in and letting him have what he wants when, long term, its not the best solution. To take him downstairs is just enabling him. And, you are prolonging the situation.
This is where tough love kicks in. You need to stand strong and make him stay in his room/bed. Like Rachel said, the Supernanny technique works pretty well. Although I altered it a little for my DD initially. When they get out and are making demands, instead of putting her back in bed silently, I tell her why she is not getting what she wants and let her know that if she continues to get up, I will continue to put her back. Then the games begin. So you have to say what you mean and do what you say! After that, you should just caringly and silently put him back into his bed each time. The first couple of nights may be sleepless but you are establishing the boundaries and rules for him and eventually he will realize his efforts are unsuccessful and he'll give up trying.
Its hard as the parent, but if you take the easy way out (enabling) you'll regret it later. Resolve to have a couple of nights w/o sleep and then stay strong!!
Good luck!
D.