Many people are unaware of the fact that it is possible to decompile and disassemble almost all types of Windows Exe-files.
What is a Decompiler
A decompiler is the name given to a computer program that performs the reverse operation to that of a compiler. That is, it translates a file containing information at a relatively low level of abstraction (usually designed to be computer readable rather than human readable) into a form having a higher level of abstraction (usually designed to be human readable).
Free and Open Source Decompilers for Windows
REC 2.1 - Reverse Engineering Compiler
REC is a portable reverse engineering compiler, or decompiler.
It reads an executable file, and attempts to produce a C-like representation of the code and data used to build the executable file. It is portable because it has been designed to read files produced for many different targets, and it has been compiled on several host systems.
RecStudio offers a modern user interface to REC's interactive mode. A command line version is available for Linux and Solaris hosts.