I read a good article over at CatholicCulture.com on the Church's teaching on salvation outside the Church. The article was describing correspondence between the author and a protestant, who was questioning Catholic teaching on whether a Muslin can be saved. My favorite quote was "...that the Church teaches that any person who, responding to the grace he has been given, seeks to know God and do His will (or if he has no opportunity to know God, at least seeks to know the good and to do it) may be saved". This approach to salvation was not acceptable to the protestant, primarily do to individual interpretation of scripture. The article goes on to discuss the necessity of the magisterium in guiding our interpretation of scripture.
The article provides a great road map on how to discuss this issue with people. You can find the article here.