Thanks Funkinator;
That is what I was meaning as well, being able to differentiate between the notes and progressions, by listening. My Brother plays the keyboard, and he usually plays the bass lines on the keys and then dictates to me what he is playing. I write it down, and then try to keep up.
However, often he is not avaliable, and I was wanting to know a bassists perspective of being able to hear what is being played.
I found a site online called perfect pitch... that is a pitch training course, I think I am going to look into that or... a CD set I found called "Complete Bass by Ear"
Thanks again for you post Funkinator, it was encouraging...to know that with time and effort it can be achieved.