Is anyone familiar with soundproofing options? Swan's End is a semi-detached house, and there are two walls in my house where the sound comes through from my neighbours' place. I'd like some advice on how to soundproof existing plaster walls. →[More:]

The two shared walls with noise issues are in the (first floor) living room and the (second floor) middle bedroom. The living room has been renovated without soundproofing, and I don't find the noise a serious issue in that room, so it can wait until the next time I repaint it, which is likely a good seven years away. Noise is much more of a problem in the middle bedroom so I'd like to do it when I renovate it after I finish my current project (the hallways). I remember how when I first moved in to Swan's End I was sleeping in the middle room while my bedroom was being painted, and my neighbour woke me up one night when she began screaming at her husband at three in the morning. I often hear yelling/screaming coming through that wall, and music. (My neighbour told me herself she has never heard any sound from my house.)

I don't want to take down the existing wall, which I believe to be plaster and studs with a layer of brick between the houses. I want whatever new surface I wind up with to be paintable. I need to think about how to get the supplies home from Home Depot as I don't have a car, so if this is something I need delivered I'd like to order the supplies when I order new flooring for the hallways. What are my options?