Thought I'd take a stab at answering Marks questions (from 29 Dec 08):

1) Why is Mary singing to the "holy virgin" (alma k'dosha)?

The "virgin holy" refers to the person who is speaking. I think the verses are Mary talking to Jesus and the chorus is the lullaby she sings.

2) Wouldn't Mary have known "why they came in praise of thee"?

Yes. But an adult will often playfully ask a question to which he/she knows the answer when talking to a child (e.g., a mother might say, "Who's that?" while pointing to her husband). It's another sweet, mother-and-child moment in the song.