Thanks to all who responded to this off-topic prompt for help.  It
turns out that MSD incorrectly reported the UART as an 8250.  In
reality (HP provided this answer), it is an integrated 16450.  Either
way, the serial connection is limited to a one character buffer.
 
The HP model I specified in my initial post (HP Vectra 486/25N) only
has 3 expansion slots.  In some cases, all 3 are full.  We're moving
ahead with the serial card and have confidence it will work.
 
So much for trying to save a few bucks on a slimline workstation!
 
Regards,
 
--- John Joerger  ([log in to unmask])
  The pessimist says the glass as half empty.  The optimist says the
  glass as half full.  The Re-engineer says you have twice as much
  glass as necessary!