Hugh. Will cover this in my feb blog. For now, Mario has answered your questions. A couple things to add. You don't need the polyphonic version to do this. Just the cheapest version. The trial version will also let you do this (for a month).

It is best to tune and adjust the timing of your vocal before saving as a midi track. And as said before, make sure the tempo is right. Then open up the midi file in your daw and as Mario said you will need to adjust a few bad notes. I use the piano roll to do this (I'm not so good with the score).

Will do that blog post..,,

Hundreds of Backing Tracks here Band-in-a-Box Files