Adding a field value, based on another field

On my table I have 4 fields - book ref, book number, book name, contractor
the form that feeds to this field has a multiple column option box which 
shows all 4 entries ( so people can pick one )
However, only the book ref saves onto the table - the other 3 values dont
I have 3 other text boxes on my form which updated based on the values 
chosen in the book ref option box - but these values dont then feed to the

table.
How do i do this ?