This treasury music is their birthright heritage as Catholics, as much as Martin Luther's hymns are for Lutherans, Russian chant is for the Russian Orthodox, Gospel songs are for revivalist congregations, and a cantor's Hebrew chant is for Jews, et cet. All religious communities with a long history and that use music in their worship appear to develop a distinctive musical brand, and this body of music is what is distinctively ours. You are trying to empower the faithful in your community to cease being strangers with what is theirs by right. They should no more be strangers to [insert name of your basic chant of choice] than Lutherans should be strangers to A Mighty Fortress Is Our God or Jews to the Kol Nidre.

1. Don't be guilty of plodding chant. People may associate chant with plodding versions that were once balefully common. (If your church's acoustic is not resonant, however, there's not much you can do to make chant sound as inviting as it should be.)
2. Chant doesn't have to be only in Latin. It may be good to avoid having chant being experienced only in its Latin form. (You may have to teach people how to pronounce the Latin, and if it's not an obvious text from the ordinary, be sure to provide translations as a basic gesture.)
3. Really? Children are well known for taking to simple chant like fish to water. (You might start by choosing chants that can be sung well by your most intimidated choristers. And, given the ever-growing musical illiteracy among people these days, you may have to teach by example - antiphonal repitition, et cet.)
4. No, actually, it's not.

Most of all, don't preach at them about the value of this music. You should be aligning yourself with them, rather than over them, as it were.

All of Liam's advice is sage.
Also, since your priest is on your side, you might ask him to say a few encouraging words to the people before making your presentation.
If they have no doubt that their pastor really wants chant, their attitude will be much more positive.
Teach chant by singing, never with an instrument. People need to hear the sounds, words, diction and rhythms that they are supposed to sing with their voices.
Emphasize how the chant exists to illuminate the text and follows the rhythm of the words.
Tell them, show them, how joyful and worshipful it is.
Help them to realize that chant is a seminal aspect of their Catholic culture, of being Catholic.

Another approach is not to talk to them about it at all, just sing it and invite them to sing it after you, with a word of two about the meaning of the words...in other words, the less you say, the less they have to complain about.

This is how the vernacular Mass music was introduced. "Today we are singing" seems to have succeeded.

But all this is wasted if the pastor does not thank them for participatingm even if they do not.

And if no one except the schola comes, it's still not a waste of time!

Talking about chant probably won't be very effective. Put something in the bulletin like "did you know?" and perhaps a paragraph or two about the patronage of sacred music or something like that.

The effect of chant on the humors is said to depend on its Mode (scroll down for chart). Try Mode VIII chants if you want to cure people's depression.

Thanks, everyone, for the insightful and generous comments!

Last year I did a "introduction to chant" workshop for the parish, and it worked out quite well. I'm going to repeat that in a couple of weeks. Granted, it only speaks to the people who are OPEN to chant, but brick by brick...

The pastor is supportive but not overly complimentary. I'll take what I can get, but I don't expect him to say more than 10 words about the music at the Mass. I tested that with him yesterday, and didn't sense that he wants to personally take a more visible role - he's worried about the larger issues of backlash against other changes he's making, and will need to make in connection with the new Missal.

I've been using various Chabanel psalms for a couple of years now, and have been composing my own Alleluias based upon the Latin text in the Gregorian Missal. I try to have a mixture of traditional hymns, Latin chants, and English chants. This year I'm going to attempt incorporating the Communion chant of the day, albeit with some simplifications for our schola.

I have occasionally put articles in our bulletin but it's hard to know how much impact that has - the only thing people ever comment about is trivial errors.

Thanks all, and keep the suggestions coming!