@croydon - If someone is really worried about that and doesn't have their heart set on a particular instrument, there's always an electronic instrument, like the keyboard or an electric guitar. You can set them up so that only you can hear what's going on, through headphones and then you can play as much as you want without disturbing anyone.
I have also found that there are some amazing courses online for people to use. There are even university level courses that have been released since most universities recognize that people go there for the degree and it costs them nothing to release the program into the internet.
I wouldn't start with one of those courses, though, I would find a nice and simple lesson on how to read sheet music and some basic musical theory first and then go from there.