I'm just going to add to what I've said that at some point, you are going to
have to bite the bullet on this and you may be at that point.
I don't have any ideas about solving the problem and it may be difficult
unless someone actually has experience with this specific application unless
it was custom made for you in which case it might be impossible but
something might turn up in response to your post. You also might want to do
a search on Google,
www.google.com to see if you can find this issue or
something close and see how it was handled.
That said, if you are unable to find a resolution, you do still have the
option of what I wrote in the last paragraph of my initial response with
regard to dual booting with a version of Windows or even DOS in which you
know the application will function.
Something else to consider, if the data files are exportable in a format
that could be imported into a database or spreadsheet, you might then look
for a Windows based program, preferably an XP compatible application that
could import the data and let you continue with the new application. You
are going to face this at some point because DOS and DOS applications are
becoming ever more obsolete with each new upgrade and iteration of Windows.
An alternative might be to purchase an older computer that will run DOS or a
version of Windows with DOS and use it specifically for this application.