A few questions (sorry, I don't have these bar code fonts or a scanner here
so can't experiment)...
What actually works (and fails) when you use these barcode fonts, e.g.
a. does a barcode on its own in Word (no mailmerge involved) work?
b. does a barcode + JPG in Word (no mailmerge) work?
c. does a barcode on its own (no JPG, using mailmerge) work?
d. if the barcodes do not work from Word at all, do they work when printed
from any other Windows program (e.g. Wordpad?)
If they don't work from /anything/ I'd suggest that either
- there is something wrong with the way you are constructing the barcodes.
I would have thought you have to spell out every element of the barcode as a
seperate character. Or
- the fonts are not up to the job (seems unlikely) or
- the printer is not up to the job
If they work in (say) Wordpad but not in Word, I wonder whether there is a
formatting problem in WOrd. Perhaps the font size or character spacing need
to be set in a particular way. Or maybe you need to change one of the
per-document Compatibility options in Word (open your document and look
through the options in Tools|Options|Compatibility).
If they work in Word but not with a nearby JPG or post-merge, I'd still
suggest a formatting problem as the likely culprit - perhaps the results do
not have the same paragraph style as the material in the mail merge main
document or some such.