/3/ - 3DCG

the best way to do this in max is to delete all but 1 of what you want to re use before you UV. So say you have 2 arms on a character - delete one. You have 6 lug nuts holding your wheel on your car - delete 5. Delete half of your face if you want that mirrored but be careful because you will get a very noticeable butterfly effect. anything down the center of a character can be problematic because it will look like a rorschach test. you can fix this by adding any extra object and shove it in there to break the pattern.
After you have Deleted all but 1 of what you want to mirror/duplicate then go ahead and UV it. when you are done and go to duplicate your objects the UV's will be directly on top of each other and you wont have to fuck with them or get them to line up. Doing this also helps to give you as much space as you possible can in your UV layout
The pic is a mod I did on Nisha from BorderLands. notice how they cut down the back of her body and kept it whole to reduce the butterfly effect but they still duplicate the arms/legs/feet and any accessories
I would suggest doing it this way if you are making a model for any newer gen but games like LOL and DOTA2 you pretty much have to cut the entire model in half because they dont allow anything above 512