you can combine the fields that you want to printed as barcode in a formula.
create a formula which contains all fields that you want.
e.g.: trim({tbl.partno})+trim({tbl.itmcode})
and change the font with barcode font.
some cases, you will need to add '*' in front of this formula and at the end of it.
so, it will be printed as '*'+trim({tbl.partno})+trim({tbl.itmcode})+'*'
hope it help.