How do you model units with 3ds max?

I was wondering, is it possible to export things from one unit to another with 3ds max 7? I had a look at some tutorials but I'm still confused. I've never modeled or did anything like this before. What I wanted to do was give barbarian Swordsmen the leather armour the barb peasants wear.

Have a look at the head swapping tutorial in the buildings and units section of the scriptorium

It describes exactly that.

If all you want to do is change the texture on the unit, you might get away with just re-painting the texture, and not have to edit the CAS file at all.

When I try to open a file like Barbarian Peasants it says it doesn't recognise it or something like that.