Rodolfo,
Well, OK, I admit. This is not a free solution, but close

And
also, I've never seen an EAN-13 generator for free, so chances are you
won't find one, either.
We offer BarCodeWiz ActiveX, which is a control (plug-in) that allows
you to create many types of barcodes, including EAN-13. The cost is
only $95 for a single user license. There is a free demo, which
includes several examples of use in Access 2000 (on reports and
directly on a form).
http://www.barcodewiz.com/demo.asp
This page shows step-by-step instructions (with screen shots) on how
to set it up in Access:
http://www.barcodewiz.com/screenshots_Access2000.asp
Now, although this page shows BarCodeWiz ActiveX, the procedure is
similar in any component you might use.
If you have any questions, please don't hesitate to ask.
Alek Szymanski
Add barcodes to your programs and documents
http://www.barcodewiz.com