Andrzej.
What version of REFOX do you have? What version of Foxpro was the application compiled in?. Was you application a) encrypted using Refox and/or b) compressed at any time?
If so then REFOX is you best bet (i haven't found another decompiler), try and get the latest version as this will decompile upto VFP6, even the demo version. Look at
http://www.xitech-europe.co.uk/ReFox.html. They are up to version 8.
IF it was encrypted then you need to find someone with the pass-key or the job is pointless (unless of course you know about dencryption)
Sorry cannot be any more helpful at the moment but will do some investigation from this end.
Chris