If you have a 71 and a Zenwand, you have all you need to read bar codes.
Type BARCODE$ into the 71 at the prompt, press enter, and scan the barcode on anything nearby, such as a cereal packet or a book. The results should appear in the display. Do something like A$=BARCODE$, and the result will end up in A$.
I don't have a manual for Zenwand, but I'm fairly sure there's a bunch of features for handling errors, extracting checksums and so forth. I'm also fairly sure it doesn't decode HP-41 barcodes, but I might be wrong -- I think there is a feature to extract all the bar-by-bar information from any barcode without decoding it, so it's probably possible to write your own decoder anyway. :-)
If you want to use it, you really need to get the manual -- among other things, it includes a little one-line BASIC program that has to be in memory, or some feature doesn't quite work right. Again, I don't remember the details.
If you have an HP2225B HP-IL ThinkJet printer, you can also print barcodes using Zenwand's BCPRINT program. It only includes a driver for the HP2225B HP-IL ThinkJet, but it's possible to add other printer drivers -- I don't know if the information on how to do this was ever released, though.