Thanks! I have a 64-bit Windows machine, so tried Legacy 4.0 -- but get an error ("Unrecognized database format").
I know the program I had was built in 1996 (based on the last modified date of the executable) and my tree data was last modified in 2002.
The PDB and PDX data files are the ones with the names.
On another forum online, I just found that these files are used Europress Family Tree -- not sure if that helps, if anyone still has that program.