Posted 14 February 2009 - 02:03 PM
It depends entirely on how the setup.exe file was created. Some, like you said, can be opened by Winrar. This is because the setup.exe file is actually a self-extracting archive which extracts the real setup.exe and then runs it. Most setup.exe files, however, either don't do this or they use a proprietary format, or they may use the WISE installer framework included with Windows (or another framework altogether.)
Thus, there is no single "universal" unpacker for setup.exe files as there is no "universal" format for creating them.