ok, i agree you definatly need to introduce them away from your home, that way it's nutral teritory. get them used to each other then take them back home at the same time.
also it would be a good idea to get a blanket or something similar from your house, something containing your scent and rub it over the new pup, that way he will smell familiar to your dog and be more acceptable
let us know how you get on, remember these things can go three ways
1. your pup will be accepted straight away and you'll wonder why you were worried
2. it may take some time but eventually it will work out, if your dog is a bit snappy or growls a bit, keep them apart unless supervised, its just them establishing heirachy.
3. all out war, may still work out but you need more advice from a trained dog psycogist
you have one dog who is established in the home, he should be the boss, help him to establish this fact. make sure you feed him first and don't feed the pup till he's finished. if its obvious he's the boss to both of them there should be little conflict and not too much hassle
good luck