I'm looking for software that provides support for robotics physical simulation. My impression is that "physics simulators" for graphics / games do not provide what I'm looking for. I want to input detailed control information and have the simulator actually perform a very good approximation of what a real robot of similar design would do in response.

I assume that there is nothing advanced enough (or cheap enough) to do this sort of thing using point and click methods for assembling robots from concept / imagination. But I'm looking for software to start with that's as close as I can get to that ideal; preferably Open Source; hopefully simulating things like responsive joints and taking weight distribution of components into consideration. (To understand that easily, imagine a humanoid robot with arms and legs and maybe servo motors at joints.)

I'd even be interested in learning more about products that can do the job, even if they are costly. I just don't see the possibility of buying an expensive product right now. But if you know about something, I live by the rule that all knowledge is good knowledge.