1. load a figure into your scene
2. load a prop into your scene
3. select the body part you wish to replace
4. go to Object>Replace Body part with Prop
5. choose the prop in your scene from the menu that will appear

Bingo. You're done.

There are also other methods that can be very useful depending on your actual goals, but these tend to get progressively more difficult and will involve obj editing, cr2 editing and quite possibly some virgin sacrifices. We've had our fair share of them all. :p -Les