Convert .exe to Source code

Summary: We have an EXE application we would want to be converted to a working C/C++ or VB source code. Background: We currently have a .EXE application. It is a windows application but was written for windows 3.x (16 bit) though it still works on Windows XP. However, the application does not work on Vista, it simply crashes. It also has a lot of limitations we have been managing for a while. We need to decompile the application back to source code to enable us make adjustments and upgrade it.