Depending on printer you have two methods - either you have a printer that support barcodes (as any other font) or you have a label printer.
BARCODEFONT ON LASERPRINTER
In printinfo-files under Baan lib you could specify userfonts, by adding escape-sequences in the specific printer-file. If you look into the printer-file definitions you will see defintion for boxes, font-changes etc.
Add a user-font to your printinfo-file - a little tricky but managable. In your report you will call for your "user"-font and you will have your barcode.
If you have a label-printer, then you create a script that will be called as part of printing. It is defined in the device-definition. Think I used the ASCII-format. In the device-defintion you enter ASCII/script_File_name. You have to check format for type of output and how to call a unix-script. Anyway - in the script you can use an ordinary "lp-command" to print the file to your label-printer.