Ian --

I've tried practicing by putting the various parts into a program called "Noteworthy Composer" -- that highlights each note and lyric syllable as it is played, so I can read along with one musical line and try to stay "on track" (pun only partly intended ;-)) with that. And that helps. But just singing one note while hearing another isn't quite the same as singing one *word* while hearing another...

Hence, the second part of my question: "How do you encourage your friends to join in?"

Singing rounds, I seem to recall, was a natural thing to do for us when we were kids, but for adults... seems about as respectable as playing the kazoo! ;-)