It depends if you can find msvb60.dll (I think that's what it's called) for a Mac. Since this is visual basic, you need to have several DLLs to interpret function calls. I don't know if you can find it for a Mac or not. That goes for unix, linux, and any other operating system you can think of that's not windows.
If no such libraries exist, we'd have to port it to a new language. Which, let me tell you, is about the hugest pain imaginable. Not to mention we lose any forms, windows, etc. that we designed. On the other hand, it would run alot faster.