Jack, when I coach people who are going to read the Scriptures to the congregation, I tell them they should read as if they're singing the words without a particular tune. Same goes for telling a joke, and especially for telling a children's story. The spoken word, if spoken well, has most of the characteristics of singing. So, if you can teach people to recite or read something, you can teach them to sing.
I think it's important to choose your carefully when you want people to sing. If you can find a simple tune that makes people feel they sound "just wonderful," in all likelihood, they WILL sound wonderful. Gregorian chant is like that - simple melodies in a singable key that sound really great. Those old monks knew what they were doing. Pick a song that doesn't fit the audience, and you'll be singing a very lonely solo.
And Alice, you sure are right about choosing appropriate keys. At the song circle I attended Friday, the woman who plays the guitar played everything in a key suited to her alto voice. To match it, I had to sing at either the top or the bottom of my range. My throat still hurts. I was called on to sing a request at the church Oktoberfest Saturday night, and I could hardly get any sound out. The congregation was in a great mood by then, so they helped. The song? "In Heaven There Is No Beer." Appropriate for a church function, don't you think? That followed half of Peter's principles (drink and Christmas).
-Joe Offer-