I downloaded this program, and I have to say, this is nice. I was also a programmer for our team... and I plan on majoring in Computer Science when I enter college this fall, and from my point of view you deserve mad props for this. This year, I worked on a mathematics parsing program which would do things like 2.5^(2*-4) and whatnot in correct order. Considering that my big glorious project is actually something you will implement as one component of your big initiative that is emulationFIRST, I really have no place to make suggestions, but I'll do it anyway.
1) Parser programs are very OOP-friendly. I did mine in C++ and built it around classes. The power in this is that you can make a general token class a base class and have all the different kinds of tokens, like reserved words or math operators, different derived classes. But what I love about C++ in this case is try, catch, and throw. Whenever I have a parsing error I just throw an exception and it gets me right where I want to be in my program flow. I understand that your deeply entrenched by now in the structure of your program and a conversion to classes would be too time-consuming for what it's worth. Plus you might not have the compiler for it.
2) Real time???????? You can use the game ports in a computer to test it out. I know it's a stretch and it's probably better to somehow do it from the OI, but hey, it's just an idea.
3) If you go GUI, my suggestion is compile the C to DLL and have a VB front-end slide right on top of it. This way, you could possibly implement suggestion #2. But, this is platform limited, and I don't know if you have the compiler for it. This is just the easier way I would do it; if you do it in C, then all the more respect to you.
Again, props. I saw your web site, good luck with the co-op and with RIT. I'll read some more of this code.... looks yummy.