Like Graham, I'm outside the US and don't have much practical experience of
Word's Barcodes, but this is what I do know...
First, you need to use Mailmerge (specifically a Lebel mailmerge, not the
Envelopes and Labels function.
You should develop the layout (fields and text) you need in the first label,
then use the Propagate labels function to copy your tested layout to the
other labels.
You will probably need to enter the field codes manually into the label, so
use Alt-F9 to toggle between field code and field result views and ctrl-F9
to enter the special field braces "{}". Everything else is plain text.
Ensure that your locale is set to U.S. English in Regional options,
otherwise the barcode field will not work whatever you do. (If you are in
the U.S. this would typically be the default setting).
US POSTNET barcodes are constructed from two pieces of information which you
will need in your data source:
a. a number in a street address
b. a 9-digit ZIP code
The BARCODE field requires that the 9-digit ZIP is in 5-4 format (with the
hyphen).
In your label you typically need a BARCODE field that looks like:
{ BARCODE "{ MERGEFIELD "street address" }¶
{ MERGEFIELD Postcodefield }" \u }
(The ¶ is just a normal paragraph mark that you will see if you press Enter
after { MERGEFIELD "street address" }
and click the ¶ symbol in Word's toolbar).
However, the last 2 digits of the BARCODE may not be generated from a Street
address in all
cases, so you may need to do something more than just { MERGEFIELD "street
address" }. You may find the following articles useful:
WD2000: How to Read Postal Bar Codes
http://support.microsoft.com/default.aspx?scid=kb;en-us;214181
and the article referenced in there:
WD2000: USPS Changes Postal Bar Code Requirements for Multi-Unit Buildings
http://support.microsoft.com/default.aspx?scid=kb;EN-US;220548
NB, The barcode field inserted by the Envelopes/Labels option uses a
slightly different approach which is to bookmark the whole address and use
{ BARCODE bookmarkname \b \u }
I would have also have a look at:
WD97: Word Assigns a Delivery Point Bar Code (DPBC) of 99:
http://support.microsoft.com/default.aspx?scid=kb;en-us;197008