I've only had a quick look at Polonius, but it's not even remotely endian safe. I'll have to rewrite/add the loading and saving functions before a non-Intel version would be possible. I don't really care enough to fix all of that right now but I'll try and get to it at some point. It all needs to be converted to use standard type sizes anyway (ie, "int32_t" rather than "int"), since there is no point in assuming crap like that for a new app. Just because it works on something that's not Windows x86 based doesn't make it cross-platform.
Hmm, well I used wxWidgets for it, and did have to make some mods to get it working under L64 (As far as the VP library goes, AFAIK the GUI had no big issues).
I'd be interested in seeing the source if/when you do all that crossplatform stuff, although Polonius (Being my second significant wxWidgets project) has some minor issues. Such as, right-clicking and middle-clicking not working at all, and no Unicode support, and it may still hang on exit under Linux. The list tabs also don't resize very well, but I'm not too concerned about that.
As far as vplib goes, I'd probably want to try and get rid of that dependency on virtfile if I were rewriting it today. The abstraction is mostly used to load, read, and write the VP index and isn't really necessary, it could be done with some hard-to-read but fast C.