Wow,
Wow! San Clemente to Pittsburgh! You are in for some climate AND culture shock! I have family in San Clemente and would move there in a heart beat if it weren't for the earthquake and wild fire threats. Beautiful town. Great vibe. Pretty much utopian weather.
Anyway, Xavier... ignore all of the comments about Duquesne the neighborhood. It is nowhere near Duquesne the school. The walk to Duquesne from the South Side is quite a hike, especially in the winter, but there is a stairway from the end of the 10th street bridge up onto the Duquesne campus. If you really are set on being able to walk, I would look for places in an arc starting nearby to the south end of the 10th street bridge. If you like dive bars and the accompanying crowd of rowdies, you will LOVE the south side.
Anywhere other than Southside or a city high-rise, walking will be out of the question, but busses are decent and students can get discounted passes. If you still want to be somewhat close, Shadyside ,Squirrel Hill and Regent Square are all good choices (in that order, IMO). All are relatively safe, have shopping, restaurants, etc. nearby and are a reasonable bus ride to Duquesne.
Good luck with your move, and come see us when you get settled!
Adam