Websearch 'MS COFF', then learn assembly language (there are decent FASM tutorials on the NET), then all you need to undertand is how the final byte code (machine code) relates to the assembly language... its not far off.
http://en.wikipedia.org/wiki/COFF
http://flatassembler.net/docs.php
http://courses.ece.uiuc.edu/ece390/resources/opcodes.html
http://en.wikipedia.org/wiki/COFF
http://flatassembler.net/docs.php
http://courses.ece.uiuc.edu/ece390/resources/opcodes.html