How should I got about implementing joints in 2D? If anyone could point me to a useful website I would be very thankful. :) Thanks in advance, Mr. Big

There are actually two separate problems involved when you're dealing with joints, and you've probably heard of both of them. The easy problem is called forward kinematics. That is, if you know the angle of each joint with respect to its parent, you then use use FK to find the position of each joint in the world frame for rendering or dynamics. The reverse problem, known as inverse kinematics, is much harder. Given a set of world joint positions, you want to find the set of joint angles that satisfy those positions. Usually you aren't solving for all joint at once, just a single joint you're interested in known as the "end effector". And many times there might not even be a solution, or one that satisfies your set of constraints.

Forward and inverse kinematics in 2D are relative easy compared to their 3D counterparts, but still challenging enough. I don't know of any sites per se that offer info on IK/FK in 2D, but you can also Google around or try Wikipedia.