SoftMotion(c)2011
ModelProp
    - About
    - Creating Objects
    - CSG Tools
    - Adding Limbs
    - UV Mapping
    - Quick Parts Menu
    - Editing Objects
    - Object Properties
    - Vertex Tools
    - Animation
    - Saving & Loading
    - Register
        My 3D World
First you must select a limb from the drop down box as the parent limb.  Next you can click on the first button in the limb tools frame to tell the editor you would like to add a limb child.  Next you can click on the pick button that is flashing to manually select an object.

The object will now be connected to its parent limb.  You can now select the object and then select the limb that you just added to modify offset and rotation and scaling information.

The [+] button is to copy a limb back to a single object.
The red green colored button will swap a limb with another object retaining parent child relationships.