A Very Territorial Chihuahua And The New Dog In The House. Help?

The chihuahua isn’t exactly mine, but it lives in the same house I do. I was thinking of getting an Italian Greyhound, and before anyone says anything about that, yes, I am very capable and ready for taking care of it. Is it possible to train the Chihuahua so that he can accept that the new dog will be living in the same house as him? If so, how?