MacOS X is phasing out the metadata stuff in favor of 3-character filename extensions, so one solution is to wait a year -- your users will mostly be upgraded to X, and the problem will be gone!
>Thus they refuse to open in the original application. Are you saying that (1) when you double-click on it, it doesn't know what app to open it with, or (2) you can't open it at all? Unless the data fork is damaged, the app should still be able to open it if you first start the app and then do File>Open. Maybe you could also explain a little more about the process by which users upload their files.
