NEED HELP A.S.A.P!! Anyone who has had experience taking care of another dog!?

Ok so I am currently babysitting my God mother's dog for her for 3 weeks while she and her family are off on vacation, and I already own another dog, but there's a problem, my dog doesn't like the new puppy and well right now they're both in separate sections of the house. I need help on what to do to not only take care of this puppy that might get home sick, but help my dog and him get along so i'm not secluded in one half of the house. Please help, any ideas on how to go about this? By the way this is my first time taking care of someone else's dog.