Madamez, IMO friendship has to be about mutual respect and trying to understand each others' lives, even if they are quite different sometimes.
For example, some of my friends are way, way wealthier than I am (or am ever likely to become). In itself, this presents no problem - if however they started going on about how rich they are, Harry-Enfield like then I doubt if I'd be phoning and inviting them for coffee! As it is we hardly ever talk about money - there's no point because having lots of it means that they hardly ever have to think about it - so we talk about everything else under the sun and have a friendship I really enjoy and value.
Another one - I speak pretty fluent German, which my dh doesn't speak at all. If I tried to teach him German against his will (now there's a thought) and insisted that we would only speak German in our house, I don't think he'd be too chuffed!
So it is with religion. With my non-religious friends we talk about everything and anything else. Sometimes the subject arises, and when it does I am very comfortable talking about what it means to me to be a christian - however I'd never foist this upon my friends becaues to do so would be trampling all over them emotionally - not very nice IMO.
Discalimer - Christainity is without doubt a missionary religion. There are christians who are especially gifted at explaining the faith (I know someone who excels at this) but there is a duty upon all christians to "stand up and be counted", to acknowledge your faith as and when the opportunity asises, and not to be ashamed of being a christian.
So I am happy to be friends with people who aren't christians - however I do expect a basic respect from them, for all that I am including my faith - and I extend that same respect back to them for all that they are, including their non-belief. Otherwise it's not a real friendship, is it?