How do I get a printer that will print on both sides of the paper
automatically to do so from two worksheets in the workbook. If I have
two pages on the same worksheet it works fine or if I print to a
printer that requires the paper to be changed manually it works fine.
But it the printer handles the paper automatically it gives me two
sheets with the back side blank.

This problem annoys me too. Excel seems to treat sheets as separate
documents.

The following works for me, but it's awkward.

Print each worksheet using the "Microsoft Office Document Image Writer."
This produces an ".mdi" file for each worksheet. With both files open, it's
possible to copy pages from one into the other, merging the two into one
mdi file. Then the merged file can be printed.

For somebody doing this a lot, it might be helpful to use third-party
software like:
http://www.fineprint.com/products/fineprint/index.html