I don't know what program does Jeck Jims or other 3D modellers use, but I've used Misfit before and it does the job; you gotta learn 3 different skills to make a proper 3D model:
* Texturizing, basically giving the model colors and all that.
* Topologizing (or retopo with tris/triangles formed vertices)
* Animation, skeletal or topological, whichever you prefer, I've never used skeletal with that program, since it doesn't work very well with MD2; I also stuck with topological animation with MD3 (I won't upload any of them, they are not fresh in any way).
PS: It doesn't sound as a request but a question. I'd advice you to start playing around with other peoples md3 and making yours, not recoloring but actually modifying stuff from them (not uploading it, just using it as practice.)
Animation is kinda easy if you really pay attention to mechanics that make sense.
P.S - There is a trick with misfit to clone vertex's positions within each frame, so you could select the knees, for example and paste it to another frame, so you only animate 1 joint and mirror it to make the animation as exact as possible.