Thanks again to all for their thoughts and comments.
Microsoft sold over 400 million copies of XP and I figure if my programs work on XP, they should easily work on Win Vista, Win 7, etc. with no problem. Yes, I understand that philosophy precludes, with both the OS and the IDE, being able to take advantage of the latest and greatest features.
I do like very much the Pelles IDE as it is fast and easy to use. I'm going to stay strictly with GUI tools and thanks to the suggestions in this thread, have learned some more about how to make it do what I want it to.
This old program supposedly ran on DOS, Win95, WinNT, and Unix but I have no way to test that capability. I'm well aware of the differences between Windows and earlier programs and the effort required to convert it to an event based system. This old program, for all its complexity, has pretty simple functionality. So right now, I'm toying with creating a Windows "shell" which will call the various modules of the old program based on user menu choices. Then later on, I can convert the whole thing to a 'real' Windows program.
But I'm ahead of myself. So for now, I'll continue to plug away. Probably later on, I'll have more questions for all you forum members. Many thanks to all for helping...