I knew we were working during Whidbey to get the PE/COFF spec updated (the previously available version dated back to, I think, 1998 or so).  I noticed that it's now available on MSDN.  Not in the place I would have expected, though.

In the past it was in the Win32 development section but now it's in WHDC:

 http://www.microsoft.com/whdc/system/platform/firmware/PECOFF.mspx