Hi Jill,
It can be done using "Performance Tracks" or "Audio"
In relation to Performance Tracks, have a look at the following thread.
...link to information on how to use Performance TracksScroll down and have a read of the post from Peter Gannon. All you need to do is to create a vocal audio file, place it in the BIAB directory for the song and rename the file.
It is also possible to import the vocal as audio.
The only requirement for the above is that the vocal would need to be recorded at exactly the same tempo that the song is in BIAB.
Regards,
Noel