I have had a lot of success using Protel99SE SP6 with Wine. I found it more stable and snappier than using WindowsXP in Virtualbox. I've used Protel99SE since 2000, and have many old designs I need to support. Since the earliest days, I've not used the DDB database storage format (it uses the old JET database), although it is possible open these files in Protel with Wine, if you have installed the database packs in Wine with Winetricks.
If you can do this, it is possible to export the PCB design file in PCAD2000 ASCII format, from which one of the PCAD to KiCad converters might produce something usable. I never found the converters robust enough to use, however, although there may have been improvements made since.
All of this is not a 5 minute exercise, though.