Thanks to the gracious help of a young woman in Easy Software support,
duplex printing is once again working on my LaserJet 5. There are two key
factors in the solution:

1) The PrintPro drivers do not work with cups-1.2.x. Dropping back to the
distribution's 1.1.23 version is required.

2) Upgrade the PrintPro drivers from version 4.4.1 (vintage June 2003) to
4.5.12. This new version supports both the 2.4.x and 2.6.x kernels. And, for
those of us with a PrintPro license, the upgrade is free.

I much appreciate the suggestions and ideas from folks here. This is a
major concern removed from my must fix list.

Rich