Just to be clear, if I was going to do any kind of isoscele, I would have to go out to the backyard and dig that guy up and take his bones far, far away! :O
This old thread is the first Google result for "moi3d construct tangent", so I wanted to put a tip here that I just found out:
If tangent snapping does not work ("Tan" doesn't appear) it's probably because the point at which you started the line is part of three-dimensional geometry and the point and the circle are not aligned in the third dimension.
