How do I convert a bone composed of a point and a quaternion to two vectors and a pt?

I'm trying to visualize the bones of an MD5-Mesh file and I see that the bones are represented as a point and a quaternion. Since a quaternion only represents a rotation, I don't know how to illustrate it. So lets say I have a human model where the arms are going across the x-axis (one hand pointing in the positive direction and the other in the negative). If I have arm bones matching up with mesh, is there a "default" vector where if apply the quaternion to it, the vector would point in the same direction as the arms (and like-wise for the up vector)? Or does every model editor do it's own thing where if I had a bone pointed in the same direction, each editor would give me a different quaternion..... or am I complete wrong about quaternions or how MD5-mesh uses them for bones?