PEExplorer 

PE Explorer is a program for inspecting the inner workings of your own program, and more importantly, third party Windows applications and libraries for which you do not have source code. PE Explorer lets you open, view and edit a variety of different 32-bit Windows executable file types (also called PE files) ranging from the common, such as EXE, DLL and ActiveX Controls, to the less familiar types, such as SCR (Screensavers), CPL (Control Panel Applets), SYS, MSSTYLES, BPL, DPL and more (including executable files that run on MS Windows Mobile platform).