In the FAQ of the Boomerang decompiler (which currently only decompiles to C-code) they make a brief mention that Visual Basic exes happen to include a lot of metadata, so a Visual Basic decompiler might be able to produce better source code for Visual Basic programs than what Boomerang can give you. Since the program I'm trying to decompile might actually be a VB 6 program, do you know of any decompilers for VB6 exes?
(Don't worry this isn't for nefarious purposes. I just have to create a data file this program parses, and getting a sense of the strategy it uses to parse the file will help get the file format right.)